Jak spać w jądrze Linuksa?

Question

Czy mogę używać funkcji msleep() do uśpienia przez określony czas w przestrzeni jądra? Jeśli tak, jakie pliki nagłówkowe muszę dołączyć? #include <linux/time.h> nie wydaje się być właściwy. Czy w tym celu może jest lepsza funkcja?

Answer 1

Potrzebowałem włączyć <linux/delay.h>, aby użyć msleep w przestrzeni jądra.

Answer 2

dokumentacji jądra Linux

Dokumentacja Jądro systemu Linux w Documentation/timers/timers-howto.txt ma dobrą wybiegiem z głównych metod:

Inserting Delays 
---------------- 

The first, and most important, question you need to ask is "Is my 
code in an atomic context?" This should be followed closely by "Does 
it really need to delay in atomic context?" If so... 

ATOMIC CONTEXT: 
    You must use the *delay family of functions. These 
    functions use the jiffie estimation of clock speed 
    and will busy wait for enough loop cycles to achieve 
    the desired delay: 

    ndelay(unsigned long nsecs) 
    udelay(unsigned long usecs) 
    mdelay(unsigned long msecs) 

    udelay is the generally preferred API; ndelay-level 
    precision may not actually exist on many non-PC devices. 

    mdelay is macro wrapper around udelay, to account for 
    possible overflow when passing large arguments to udelay. 
    In general, use of mdelay is discouraged and code should 
    be refactored to allow for the use of msleep. 

NON-ATOMIC CONTEXT: 
    You should use the *sleep[_range] family of functions. 
    There are a few more options here, while any of them may 
    work correctly, using the "right" sleep function will 
    help the scheduler, power management, and just make your 
    driver better :) 

    -- Backed by busy-wait loop: 
     udelay(unsigned long usecs) 
    -- Backed by hrtimers: 
     usleep_range(unsigned long min, unsigned long max) 
    -- Backed by jiffies/legacy_timers 
     msleep(unsigned long msecs) 
     msleep_interruptible(unsigned long msecs) 

    Unlike the *delay family, the underlying mechanism 
    driving each of these calls varies, thus there are 
    quirks you should be aware of. 


    SLEEPING FOR "A FEW" USECS (< ~10us?): 
     * Use udelay 

     - Why not usleep? 
      On slower systems, (embedded, OR perhaps a speed- 
      stepped PC!) the overhead of setting up the hrtimers 
      for usleep *may* not be worth it. Such an evaluation 
      will obviously depend on your specific situation, but 
      it is something to be aware of. 

    SLEEPING FOR ~USECS OR SMALL MSECS (10us - 20ms): 
     * Use usleep_range 

     - Why not msleep for (1ms - 20ms)? 
      Explained originally here: 
       http://lkml.org/lkml/2007/8/3/250 
      msleep(1~20) may not do what the caller intends, and 
      will often sleep longer (~20 ms actual sleep for any 
      value given in the 1~20ms range). In many cases this 
      is not the desired behavior. 

     - Why is there no "usleep"/What is a good range? 
      Since usleep_range is built on top of hrtimers, the 
      wakeup will be very precise (ish), thus a simple 
      usleep function would likely introduce a large number 
      of undesired interrupts. 

      With the introduction of a range, the scheduler is 
      free to coalesce your wakeup with any other wakeup 
      that may have happened for other reasons, or at the 
      worst case, fire an interrupt for your upper bound. 

      The larger a range you supply, the greater a chance 
      that you will not trigger an interrupt; this should 
      be balanced with what is an acceptable upper bound on 
      delay/performance for your specific code path. Exact 
      tolerances here are very situation specific, thus it 
      is left to the caller to determine a reasonable range. 

    SLEEPING FOR LARGER MSECS (10ms+) 
     * Use msleep or possibly msleep_interruptible 

     - What's the difference? 
      msleep sets the current task to TASK_UNINTERRUPTIBLE 
      whereas msleep_interruptible sets the current task to 
      TASK_INTERRUPTIBLE before scheduling the sleep. In 
      short, the difference is whether the sleep can be ended 
      early by a signal. In general, just use msleep unless 
      you know you have a need for the interrupt 

Zaczerpnięte z tej niesamowitej odpowiedzi: https://stackoverflow.com/a/39921020/895245

Następny spojrzeć w komentarzu do dokumentacji każdej z tych funkcji w źródle. Np .: usleep_range:

/** 
* usleep_range - Sleep for an approximate time 
* @min: Minimum time in usecs to sleep 
* @max: Maximum time in usecs to sleep 
* 
* In non-atomic context where the exact wakeup time is flexible, use 
* usleep_range() instead of udelay(). The sleep improves responsiveness 
* by avoiding the CPU-hogging busy-wait of udelay(), and the range reduces 
* power usage by allowing hrtimers to take advantage of an already- 
* scheduled interrupt instead of scheduling a new one just for this sleep. 
*/ 
void __sched usleep_range(unsigned long min, unsigned long max) 

LDD3 7.3. Delaying Execution to kolejny must-have zasobu.

Minimalny Runnable przykłady

Wreszcie pisać własne minimalne testy, aby je wypróbować!

• usleep_range przeze mnie
• http://www.zarb.org/~trem/kernel/wait2s/ zawiera kilka (ewentualnie stare?) Przykłady