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modify URLs that contains timers-*.html
This commit is contained in:
Dongliang Mu
@@ -20,7 +20,7 @@ clocksource_select();
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...
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mutex_unlock(&clocksource_mutex);
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```
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出自 [kernel/time/clocksource.c](https://github.com/torvalds/linux/master/kernel/time/clocksource.c) 源文件。这段代码来自于 `__clocksource_register_scale` 函数，此函数添加给定的 [clocksource](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/timers-2.html) 到时钟源列表中。这个函数在注册时钟源列表中生成两个不同的操作。例如 `clocksource_enqueue` 函数就是添加给定时钟源到注册时钟源列表——`clocksource_list` 中。注意这几行代码被两个函数所包围：`mutex_lock` 和 `mutex_unlock`，这两个函数都带有一个参数——在本例中为 `clocksource_mutex`。
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出自 [kernel/time/clocksource.c](https://github.com/torvalds/linux/master/kernel/time/clocksource.c) 源文件。这段代码来自于 `__clocksource_register_scale` 函数，此函数添加给定的 [clocksource](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/linux-timers-2.html) 到时钟源列表中。这个函数在注册时钟源列表中生成两个不同的操作。例如 `clocksource_enqueue` 函数就是添加给定时钟源到注册时钟源列表——`clocksource_list` 中。注意这几行代码被两个函数所包围：`mutex_lock` 和 `mutex_unlock`，这两个函数都带有一个参数——在本例中为 `clocksource_mutex`。
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这些函数展示了基于[互斥锁 (mutex)](https://en.wikipedia.org/wiki/Mutual_exclusion) 同步原语的加锁和解锁。当 `mutex_lock` 被执行，允许我们阻止两个或两个以上线程执行这段代码，而 `mute_unlock` 还没有被互斥锁的处理拥有者锁执行。换句话说，就是阻止在 `clocksource_list`上的并行操作。为什么在这里需要使用`互斥锁`？ 如果两个并行处理尝试去注册一个时钟源会怎样。正如我们已经知道的那样，其中具有最大的等级（其具有最高的频率在系统中注册的时钟源）的列表中选择一个时钟源后，`clocksource_enqueue` 函数立即将一个给定的时钟源到 `clocksource_list` 列表：
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@@ -409,7 +409,7 @@ head | 7 | - - - | 7 | tail
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* [Concurrent computing](https://en.wikipedia.org/wiki/Concurrent_computing)
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* [Synchronization](https://en.wikipedia.org/wiki/Synchronization_%28computer_science%29)
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* [Clocksource framework](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/timers-2.html)
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* [Clocksource framework](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/linux-timers-2.html)
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* [Mutex](https://en.wikipedia.org/wiki/Mutual_exclusion)
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* [Race condition](https://en.wikipedia.org/wiki/Race_condition)
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* [Atomic operations](https://en.wikipedia.org/wiki/Linearizability)
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@@ -104,7 +104,7 @@ int down_timeout(struct semaphore *sem, long jiffies);
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`down_killable` 函数和 `down_interruptible` 函数提供类似的功能，但是它还将当前进程的 `TASK_KILLABLE` 标志置位。这表示等待的进程可以被杀死信号中断。
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`down_trylock` 函数和 `spin_trylock` 函数相似。这个函数试图去获取一个锁并且退出如果这个操作是失败的。在这个例子中，想获取锁的进程不会等待。最后的 `down_timeout`函数试图去获取一个锁。当前进程将会被中断进入到等待状态当超过传入的可等待时间。除此之外你也许注意到，这个等待的时间是以 [jiffies](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/timers-1.html)计数。
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`down_trylock` 函数和 `spin_trylock` 函数相似。这个函数试图去获取一个锁并且退出如果这个操作是失败的。在这个例子中，想获取锁的进程不会等待。最后的 `down_timeout`函数试图去获取一个锁。当前进程将会被中断进入到等待状态当超过传入的可等待时间。除此之外你也许注意到，这个等待的时间是以 [jiffies](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/linux-timers-1.html)计数。
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我们刚刚看了 `信号量` [API](https://en.wikipedia.org/wiki/Application_programming_interface)的定义。我们从 `down` 函数开始看。这个函数是在 [kernel/locking/semaphore.c](https://github.com/torvalds/linux/blob/master/kernel/locking/semaphore.c) 源代码定义的。我们来看看函数实现：
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@@ -340,7 +340,7 @@ static noinline void __sched __up(struct semaphore *sem)
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* [deadlocks](https://en.wikipedia.org/wiki/Deadlock)
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* [scheduler](https://en.wikipedia.org/wiki/Scheduling_%28computing%29)
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* [Doubly linked list in the Linux kernel](https://xinqiu.gitbooks.io/linux-insides-cn/content/DataStructures/dlist.html)
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* [jiffies](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/timers-1.html)
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* [jiffies](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/linux-timers-1.html)
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* [interrupts](https://en.wikipedia.org/wiki/Interrupt)
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* [per-cpu](https://xinqiu.gitbooks.io/linux-insides-cn/content/Concepts/per-cpu.html)
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* [bitmask](https://en.wikipedia.org/wiki/Mask_%28computing%29)
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@@ -4,7 +4,7 @@ Timers and time management in the Linux kernel. Part 2.
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Introduction to the `clocksource` framework
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--------------------------------------------------------------------------------
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The previous [part](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/timers-1.html) was the first part in the current [chapter](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/index.html) that describes timers and time management related stuff in the Linux kernel. We got acquainted with two concepts in the previous part:
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The previous [part](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/linux-timers-1.html) was the first part in the current [chapter](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/index.html) that describes timers and time management related stuff in the Linux kernel. We got acquainted with two concepts in the previous part:
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* `jiffies`
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* `clocksource`
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@@ -92,7 +92,7 @@ Within this framework, each clock source is required to maintain a representatio
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The clocksource structure
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--------------------------------------------------------------------------------
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The fundamental of the `clocksource` framework is the `clocksource` structure that defined in the [include/linux/clocksource.h](https://github.com/torvalds/linux/blob/master/include/linux/clocksource.h) header file. We already saw some fields that are provided by the `clocksource` structure in the previous [part](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/timers-1.html). Let's look on the full definition of this structure and try to describe all of its fields:
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The fundamental of the `clocksource` framework is the `clocksource` structure that defined in the [include/linux/clocksource.h](https://github.com/torvalds/linux/blob/master/include/linux/clocksource.h) header file. We already saw some fields that are provided by the `clocksource` structure in the previous [part](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/linux-timers-1.html). Let's look on the full definition of this structure and try to describe all of its fields:
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```C
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struct clocksource {
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@@ -197,7 +197,7 @@ That's all. From this moment we know all fields of the `clocksource` structure.
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New clock source registration
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--------------------------------------------------------------------------------
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We saw only one function from the `clocksource` framework in the previous [part](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/timers-1.html). This function was - `__clocksource_register`. This function defined in the [include/linux/clocksource.h](https://github.com/torvalds/linux/tree/master/include/linux/clocksource.h) header file and as we can understand from the function's name, main point of this function is to register new clocksource. If we will look on the implementation of the `__clocksource_register` function, we will see that it just makes call of the `__clocksource_register_scale` function and returns its result:
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We saw only one function from the `clocksource` framework in the previous [part](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/linux-timers-1.html). This function was - `__clocksource_register`. This function defined in the [include/linux/clocksource.h](https://github.com/torvalds/linux/tree/master/include/linux/clocksource.h) header file and as we can understand from the function's name, main point of this function is to register new clocksource. If we will look on the implementation of the `__clocksource_register` function, we will see that it just makes call of the `__clocksource_register_scale` function and returns its result:
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```C
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static inline int __clocksource_register(struct clocksource *cs)
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@@ -241,7 +241,7 @@ int __clocksource_register_scale(struct clocksource *cs, u32 scale, u32 freq)
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}
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```
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First of all we can see that the `__clocksource_register_scale` function starts from the call of the `__clocksource_update_freq_scale` function that defined in the same source code file and updates given clock source with the new frequency. Let's look on the implementation of this function. In the first step we need to check given frequency and if it was not passed as `zero`, we need to calculate `mult` and `shift` parameters for the given clock source. Why do we need to check value of the `frequency`? Actually it can be zero. if you attentively looked on the implementation of the `__clocksource_register` function, you may have noticed that we passed `frequency` as `0`. We will do it only for some clock sources that have self defined `mult` and `shift` parameters. Look in the previous [part](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/timers-1.html) and you will see that we saw calculation of the `mult` and `shift` for `jiffies`. The `__clocksource_update_freq_scale` function will do it for us for other clock sources.
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First of all we can see that the `__clocksource_register_scale` function starts from the call of the `__clocksource_update_freq_scale` function that defined in the same source code file and updates given clock source with the new frequency. Let's look on the implementation of this function. In the first step we need to check given frequency and if it was not passed as `zero`, we need to calculate `mult` and `shift` parameters for the given clock source. Why do we need to check value of the `frequency`? Actually it can be zero. if you attentively looked on the implementation of the `__clocksource_register` function, you may have noticed that we passed `frequency` as `0`. We will do it only for some clock sources that have self defined `mult` and `shift` parameters. Look in the previous [part](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/linux-timers-1.html) and you will see that we saw calculation of the `mult` and `shift` for `jiffies`. The `__clocksource_update_freq_scale` function will do it for us for other clock sources.
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So in the start of the `__clocksource_update_freq_scale` function we check the value of the `frequency` parameter and if is not zero we need to calculate `mult` and `shift` for the given clock source. Let's look on the `mult` and `shift` calculation:
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@@ -448,4 +448,4 @@ Links
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* [clock rate](https://en.wikipedia.org/wiki/Clock_rate)
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* [mutex](https://en.wikipedia.org/wiki/Mutual_exclusion)
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* [sysfs](https://en.wikipedia.org/wiki/Sysfs)
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* [previous part](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/timers-1.html)
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* [previous part](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/linux-timers-1.html)
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@@ -4,7 +4,7 @@ Timers and time management in the Linux kernel. Part 3.
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The tick broadcast framework and dyntick
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--------------------------------------------------------------------------------
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This is third part of the [chapter](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/index.html) which describes timers and time management related stuff in the Linux kernel and we stopped on the `clocksource` framework in the previous [part](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/timers-2.html). We have started to consider this framework because it is closely related to the special counters which are provided by the Linux kernel. One of these counters which we already saw in the first [part](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/timers-1.html) of this chapter is - `jiffies`. As I already wrote in the first part of this chapter, we will consider time management related stuff step by step during the Linux kernel initialization. Previous step was call of the:
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This is third part of the [chapter](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/index.html) which describes timers and time management related stuff in the Linux kernel and we stopped on the `clocksource` framework in the previous [part](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/linux-timers-2.html). We have started to consider this framework because it is closely related to the special counters which are provided by the Linux kernel. One of these counters which we already saw in the first [part](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/linux-timers-1.html) of this chapter is - `jiffies`. As I already wrote in the first part of this chapter, we will consider time management related stuff step by step during the Linux kernel initialization. Previous step was call of the:
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```C
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register_refined_jiffies(CLOCK_TICK_RATE);
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@@ -441,4 +441,4 @@ Links
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* [APIC](https://en.wikipedia.org/wiki/Advanced_Programmable_Interrupt_Controller)
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* [percpu](https://xinqiu.gitbooks.io/linux-insides-cn/content/Concepts/per-cpu.html)
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* [context switches](https://en.wikipedia.org/wiki/Context_switch)
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* [Previous part](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/timers-2.html)
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* [Previous part](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/linux-timers-2.html)
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@@ -4,7 +4,7 @@ Timers and time management in the Linux kernel. Part 4.
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Timers
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--------------------------------------------------------------------------------
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This is fourth part of the [chapter](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/index.html) which describes timers and time management related stuff in the Linux kernel and in the previous [part](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/timers-3.html) we knew about the `tick broadcast` framework and `NO_HZ` mode in the Linux kernel. We will continue to dive into the time management related stuff in the Linux kernel in this part and will be acquainted with yet another concept in the Linux kernel - `timers`. Before we will look at timers in the Linux kernel, we have to learn some theory about this concept. Note that we will consider software timers in this part.
|
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This is fourth part of the [chapter](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/index.html) which describes timers and time management related stuff in the Linux kernel and in the previous [part](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/linux-timers-3.html) we knew about the `tick broadcast` framework and `NO_HZ` mode in the Linux kernel. We will continue to dive into the time management related stuff in the Linux kernel in this part and will be acquainted with yet another concept in the Linux kernel - `timers`. Before we will look at timers in the Linux kernel, we have to learn some theory about this concept. Note that we will consider software timers in this part.
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The Linux kernel provides a `software timer` concept to allow to kernel functions could be invoked at future moment. Timers are widely used in the Linux kernel. For example, look in the [net/netfilter/ipset/ip_set_list_set.c](https://github.com/torvalds/linux/blob/master/net/netfilter/ipset/ip_set_list_set.c) source code file. This source code file provides implementation of the framework for the managing of groups of [IP](https://en.wikipedia.org/wiki/Internet_Protocol) addresses.
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@@ -45,7 +45,7 @@ Now let's continue to research source code of Linux kernel which is related to t
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Introduction to dynamic timers in the Linux kernel
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--------------------------------------------------------------------------------
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As I already wrote, we knew about the `tick broadcast` framework and `NO_HZ` mode in the previous [part](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/timers-3.html). They will be initialized in the [init/main.c](https://github.com/torvalds/linux/blob/master/init/main.c) source code file by the call of the `tick_init` function. If we will look at this source code file, we will see that the next time management related function is:
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As I already wrote, we knew about the `tick broadcast` framework and `NO_HZ` mode in the previous [part](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/linux-timers-3.html). They will be initialized in the [init/main.c](https://github.com/torvalds/linux/blob/master/init/main.c) source code file by the call of the `tick_init` function. If we will look at this source code file, we will see that the next time management related function is:
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```C
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init_timers();
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@@ -142,7 +142,7 @@ The `tvec_bases` represents [per-cpu](https://xinqiu.gitbooks.io/linux-insides-c
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static DEFINE_PER_CPU(struct tvec_base, tvec_bases);
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```
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First of all we're getting the address of the `tvec_bases` for the given processor to `base` variable and as we got it, we are starting to initialize some of the `tvec_base` fields in the `init_timer_cpu` function. After initialization of the `per-cpu` dynamic timers with the [jiffies](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/timers-1.html) and the number of a possible processor, we need to initialize a `tstats_lookup_lock` [spinlock](https://en.wikipedia.org/wiki/Spinlock) in the `init_timer_stats` function:
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First of all we're getting the address of the `tvec_bases` for the given processor to `base` variable and as we got it, we are starting to initialize some of the `tvec_base` fields in the `init_timer_cpu` function. After initialization of the `per-cpu` dynamic timers with the [jiffies](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/linux-timers-1.html) and the number of a possible processor, we need to initialize a `tstats_lookup_lock` [spinlock](https://en.wikipedia.org/wiki/Spinlock) in the `init_timer_stats` function:
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```C
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void __init init_timer_stats(void)
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@@ -256,7 +256,7 @@ static void run_timer_softirq(struct softirq_action *h)
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}
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```
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At the beginning of the `run_timer_softirq` function we get a `dynamic` timer for a current processor and compares the current value of the [jiffies](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/timers-1.html) with the value of the `timer_jiffies` for the current structure by the call of the `time_after_eq` macro which is defined in the [include/linux/jiffies.h](https://github.com/torvalds/linux/blob/master/include/linux/jiffies.h) header file:
|
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At the beginning of the `run_timer_softirq` function we get a `dynamic` timer for a current processor and compares the current value of the [jiffies](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/linux-timers-1.html) with the value of the `timer_jiffies` for the current structure by the call of the `time_after_eq` macro which is defined in the [include/linux/jiffies.h](https://github.com/torvalds/linux/blob/master/include/linux/jiffies.h) header file:
|
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|
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```C
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#define time_after_eq(a,b) \
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@@ -420,8 +420,8 @@ Links
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* [network](https://en.wikipedia.org/wiki/Computer_network)
|
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* [cpumask](https://xinqiu.gitbooks.io/linux-insides-cn/content/Concepts/cpumask.html)
|
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* [interrupt](https://en.wikipedia.org/wiki/Interrupt)
|
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* [jiffies](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/timers-1.html)
|
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* [jiffies](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/linux-timers-1.html)
|
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* [per-cpu](https://xinqiu.gitbooks.io/linux-insides-cn/content/Concepts/per-cpu.html)
|
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* [spinlock](https://en.wikipedia.org/wiki/Spinlock)
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* [procfs](https://en.wikipedia.org/wiki/Procfs)
|
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* [previous part](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/timers-3.html)
|
||||
* [previous part](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/linux-timers-3.html)
|
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|
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@@ -4,7 +4,7 @@ Timers and time management in the Linux kernel. Part 5.
|
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Introduction to the `clockevents` framework
|
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--------------------------------------------------------------------------------
|
||||
|
||||
This is fifth part of the [chapter](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/index.html) which describes timers and time management related stuff in the Linux kernel. As you might noted from the title of this part, the `clockevents` framework will be discussed. We already saw one framework in the [second](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/timers-2.html) part of this chapter. It was `clocksource` framework. Both of these frameworks represent timekeeping abstractions in the Linux kernel.
|
||||
This is fifth part of the [chapter](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/index.html) which describes timers and time management related stuff in the Linux kernel. As you might noted from the title of this part, the `clockevents` framework will be discussed. We already saw one framework in the [second](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/linux-timers-2.html) part of this chapter. It was `clocksource` framework. Both of these frameworks represent timekeeping abstractions in the Linux kernel.
|
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|
||||
At first let's refresh your memory and try to remember what is it `clocksource` framework and and what its purpose. The main goal of the `clocksource` framework is to provide `timeline`. As described in the [documentation](https://github.com/0xAX/linux/blob/master/Documentation/timers/timekeeping.txt):
|
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|
||||
@@ -412,4 +412,4 @@ Links
|
||||
* [CPU masks in the Linux kernel](https://xinqiu.gitbooks.io/linux-insides-cn/content/Concepts/cpumask.html)
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* [deadlock](https://en.wikipedia.org/wiki/Deadlock)
|
||||
* [CPU hotplug](https://www.kernel.org/doc/Documentation/cpu-hotplug.txt)
|
||||
* [previous part](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/timers-3.html)
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* [previous part](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/linux-timers-3.html)
|
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@@ -4,7 +4,7 @@ Timers and time management in the Linux kernel. Part 6.
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x86_64 related clock sources
|
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--------------------------------------------------------------------------------
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This is sixth part of the [chapter](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/index.html) which describes timers and time management related stuff in the Linux kernel. In the previous [part](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/timers-5.html) we saw `clockevents` framework and now we will continue to dive into time management related stuff in the Linux kernel. This part will describe implementation of [x86](https://en.wikipedia.org/wiki/X86) architecture related clock sources (more about `clocksource` concept you can read in the [second part](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/timers-2.html) of this chapter).
|
||||
This is sixth part of the [chapter](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/index.html) which describes timers and time management related stuff in the Linux kernel. In the previous [part](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/linux-timers-5.html) we saw `clockevents` framework and now we will continue to dive into time management related stuff in the Linux kernel. This part will describe implementation of [x86](https://en.wikipedia.org/wiki/X86) architecture related clock sources (more about `clocksource` concept you can read in the [second part](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/linux-timers-2.html) of this chapter).
|
||||
|
||||
First of all we must know what clock sources may be used at `x86` architecture. It is easy to know from the [sysfs](https://en.wikipedia.org/wiki/Sysfs) or from content of the `/sys/devices/system/clocksource/clocksource0/available_clocksource`. The `/sys/devices/system/clocksource/clocksourceN` provides two special files to achieve this:
|
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|
||||
@@ -31,7 +31,7 @@ $ cat /sys/devices/system/clocksource/clocksource0/current_clocksource
|
||||
tsc
|
||||
```
|
||||
|
||||
For me it is [Time Stamp Counter](https://en.wikipedia.org/wiki/Time_Stamp_Counter). As we may know from the [second part](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/timers-2.html) of this chapter, which describes internals of the `clocksource` framework in the Linux kernel, the best clock source in a system is a clock source with the best (highest) rating or in other words with the highest [frequency](https://en.wikipedia.org/wiki/Frequency).
|
||||
For me it is [Time Stamp Counter](https://en.wikipedia.org/wiki/Time_Stamp_Counter). As we may know from the [second part](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/linux-timers-2.html) of this chapter, which describes internals of the `clocksource` framework in the Linux kernel, the best clock source in a system is a clock source with the best (highest) rating or in other words with the highest [frequency](https://en.wikipedia.org/wiki/Frequency).
|
||||
|
||||
Frequency of the [ACPI](https://en.wikipedia.org/wiki/Advanced_Configuration_and_Power_Interface) power management timer is `3.579545 MHz`. Frequency of the [High Precision Event Timer](https://en.wikipedia.org/wiki/High_Precision_Event_Timer) is at least `10 MHz`. And the frequency of the [Time Stamp Counter](https://en.wikipedia.org/wiki/Time_Stamp_Counter) depends on processor. For example On older processors, the `Time Stamp Counter` was counting internal processor clock cycles. This means its frequency changed when the processor's frequency scaling changed. The situation has changed for newer processors. Newer processors have an `invariant Time Stamp counter` that increments at a constant rate in all operational states of processor. Actually we can get its frequency in the output of the `/proc/cpuinfo`. For example for the first processor in the system:
|
||||
|
||||
@@ -410,4 +410,4 @@ Links
|
||||
* [IRQ0](https://en.wikipedia.org/wiki/Interrupt_request_%28PC_architecture%29#Master_PIC)
|
||||
* [i8259](https://en.wikipedia.org/wiki/Intel_8259)
|
||||
* [initcall](http://www.compsoc.man.ac.uk/~moz/kernelnewbies/documents/initcall/kernel.html)
|
||||
* [previous part](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/timers-5.html)
|
||||
* [previous part](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/linux-timers-5.html)
|
||||
|
||||
@@ -4,7 +4,7 @@ Timers and time management in the Linux kernel. Part 7.
|
||||
Time related system calls in the Linux kernel
|
||||
--------------------------------------------------------------------------------
|
||||
|
||||
This is the seventh and last part [chapter](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/index.html) which describes timers and time management related stuff in the Linux kernel. In the previous [part](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/timers-6.html) we saw some [x86_64](https://en.wikipedia.org/wiki/X86-64) like [High Precision Event Timer](https://en.wikipedia.org/wiki/High_Precision_Event_Timer) and [Time Stamp Counter](https://en.wikipedia.org/wiki/Time_Stamp_Counter). Internal time management is interesting part of the Linux kernel, but of course not only the kernel needs in the `time` concept. Our programs need to know time too. In this part, we will consider implementation of some time management related [system calls](https://en.wikipedia.org/wiki/System_call). These system calls are:
|
||||
This is the seventh and last part [chapter](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/index.html) which describes timers and time management related stuff in the Linux kernel. In the previous [part](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/linux-timers-6.html) we saw some [x86_64](https://en.wikipedia.org/wiki/X86-64) like [High Precision Event Timer](https://en.wikipedia.org/wiki/High_Precision_Event_Timer) and [Time Stamp Counter](https://en.wikipedia.org/wiki/Time_Stamp_Counter). Internal time management is interesting part of the Linux kernel, but of course not only the kernel needs in the `time` concept. Our programs need to know time too. In this part, we will consider implementation of some time management related [system calls](https://en.wikipedia.org/wiki/System_call). These system calls are:
|
||||
|
||||
* `clock_gettime`;
|
||||
* `gettimeofday`;
|
||||
@@ -369,7 +369,7 @@ static inline bool timespec_valid(const struct timespec *ts)
|
||||
}
|
||||
```
|
||||
|
||||
which just checks that the given `timespec` does not represent date before `1970` and nanoseconds does not overflow `1` second. The `nanosleep` function ends with the call of the `hrtimer_nanosleep` function from the same source code file. The `hrtimer_nanosleep` function creates a [timer](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/timers-4.html) and calls the `do_nanosleep` function. The `do_nanosleep` does main job for us. This function provides loop:
|
||||
which just checks that the given `timespec` does not represent date before `1970` and nanoseconds does not overflow `1` second. The `nanosleep` function ends with the call of the `hrtimer_nanosleep` function from the same source code file. The `hrtimer_nanosleep` function creates a [timer](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/linux-timers-4.html) and calls the `do_nanosleep` function. The `do_nanosleep` does main job for us. This function provides loop:
|
||||
|
||||
```C
|
||||
do {
|
||||
@@ -412,10 +412,10 @@ Links
|
||||
* [register](https://en.wikipedia.org/wiki/Processor_register)
|
||||
* [System V Application Binary Interface](http://www.x86-64.org/documentation/abi.pdf)
|
||||
* [context switch](https://en.wikipedia.org/wiki/Context_switch)
|
||||
* [Introduction to timers in the Linux kernel](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/timers-4.html)
|
||||
* [Introduction to timers in the Linux kernel](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/linux-timers-4.html)
|
||||
* [uptime](https://en.wikipedia.org/wiki/Uptime#Using_uptime)
|
||||
* [system calls table for x86_64](https://github.com/torvalds/linux/blob/master/arch/x86/entry/syscalls/syscall_64.tbl)
|
||||
* [High Precision Event Timer](https://en.wikipedia.org/wiki/High_Precision_Event_Timer)
|
||||
* [Time Stamp Counter](https://en.wikipedia.org/wiki/Time_Stamp_Counter)
|
||||
* [x86_64](https://en.wikipedia.org/wiki/X86-64)
|
||||
* [previous part](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/timers-6.html)
|
||||
* [previous part](https://xinqiu.gitbooks.io/linux-insides-cn/content/Timers/linux-timers-6.html)
|
||||
|
||||
Reference in New Issue
Block a user