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Re: [PATCH 1/3] timer: Optimize fastpath_timer_check()

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On Mon, 2015-08-31 at 08:15 -0700, Davidlohr Bueso wrote:
> On Tue, 2015-08-25 at 20:17 -0700, Jason Low wrote:
> > In fastpath_timer_check(), the task_cputime() function is always
> > called to compute the utime and stime values. However, this is not
> > necessary if there are no per-thread timers to check for. This patch
> > modifies the code such that we compute the task_cputime values only
> > when there are per-thread timers set.
> > 
> > Signed-off-by: Jason Low <jason.low2@hp.com>
> 
> Reviewed-by: Davidlohr Bueso <dave@stgolabs.net>

Thanks David and Frederic.

I want to mention that this patch has been slightly changed. As
suggested by George, those extra utime, stime local variables are not
needed anymore, and we should be able to directly call:

task_cputime(tsk, &task_sample.utime, &task_sample.stime);

---
diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c
index 892e3da..3a8c5b4 100644
--- a/kernel/time/posix-cpu-timers.c
+++ b/kernel/time/posix-cpu-timers.c
@@ -1117,16 +1117,13 @@ static inline int task_cputime_expired(const struct task_cputime *sample,
 static inline int fastpath_timer_check(struct task_struct *tsk)
 {
        struct signal_struct *sig;
-       cputime_t utime, stime;
-
-       task_cputime(tsk, &utime, &stime);

        if (!task_cputime_zero(&tsk->cputime_expires)) {
-               struct task_cputime task_sample = {
-                       .utime = utime,
-                       .stime = stime,
-                       .sum_exec_runtime = tsk->se.sum_exec_runtime
-               };
+               struct task_cputime task_sample;
+
+               task_cputime(tsk, &task_sample.utime, &task_sample.stime);
+
+               task_sample.sum_exec_runtime = tsk->se.sum_exec_runtime;

                if (task_cputime_expired(&task_sample, &tsk->cputime_expires))
                        return 1;

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[PATCH 0/3] timer: Improve itimers scalability Jason Low <jason.low2@hp.com> - 2015-08-26 05:20 +0200
  [PATCH 2/3] timer: Check thread timers only when there are active thread timers Jason Low <jason.low2@hp.com> - 2015-08-26 05:20 +0200
  [PATCH 1/3] timer: Optimize fastpath_timer_check() Jason Low <jason.low2@hp.com> - 2015-08-26 05:20 +0200
    Re: [PATCH 1/3] timer: Optimize fastpath_timer_check() Frederic Weisbecker <fweisbec@gmail.com> - 2015-08-27 00:00 +0200
    Re: [PATCH 1/3] timer: Optimize fastpath_timer_check() Davidlohr Bueso <dave@stgolabs.net> - 2015-08-31 17:20 +0200
      Re: [PATCH 1/3] timer: Optimize fastpath_timer_check() Jason Low <jason.low2@hp.com> - 2015-08-31 21:50 +0200
  [PATCH 3/3] timer: Reduce unnecessary sighand lock contention Jason Low <jason.low2@hp.com> - 2015-08-26 05:20 +0200
    Re: [PATCH 3/3] timer: Reduce unnecessary sighand lock contention Linus Torvalds <torvalds@linux-foundation.org> - 2015-08-26 20:00 +0200
      Re: [PATCH 3/3] timer: Reduce unnecessary sighand lock contention Frederic Weisbecker <fweisbec@gmail.com> - 2015-08-27 00:40 +0200
        Re: [PATCH 3/3] timer: Reduce unnecessary sighand lock contention Jason Low <jason.low2@hp.com> - 2015-08-27 01:00 +0200
    Re: [PATCH 3/3] timer: Reduce unnecessary sighand lock contention Frederic Weisbecker <fweisbec@gmail.com> - 2015-08-27 01:00 +0200
      Re: [PATCH 3/3] timer: Reduce unnecessary sighand lock contention Jason Low <jason.low2@hp.com> - 2015-08-27 01:40 +0200
        Re: [PATCH 3/3] timer: Reduce unnecessary sighand lock contention Jason Low <jason.low2@hp.com> - 2015-08-27 07:00 +0200
        Re: [PATCH 3/3] timer: Reduce unnecessary sighand lock contention Frederic Weisbecker <fweisbec@gmail.com> - 2015-08-27 15:00 +0200
          Re: [PATCH 3/3] timer: Reduce unnecessary sighand lock contention Jason Low <jason.low2@hp.com> - 2015-08-27 22:40 +0200
            Re: [PATCH 3/3] timer: Reduce unnecessary sighand lock contention Frederic Weisbecker <fweisbec@gmail.com> - 2015-08-27 23:20 +0200
  Re: [PATCH 0/3] timer: Improve itimers scalability Andrew Morton <akpm@linux-foundation.org> - 2015-08-26 05:30 +0200
    Re: [PATCH 0/3] timer: Improve itimers scalability Jason Low <jason.low2@hp.com> - 2015-08-26 18:40 +0200
      Re: [PATCH 0/3] timer: Improve itimers scalability Oleg Nesterov <oleg@redhat.com> - 2015-08-26 19:20 +0200
        Re: [PATCH 0/3] timer: Improve itimers scalability Jason Low <jason.low2@hp.com> - 2015-08-27 00:10 +0200
          Re: [PATCH 0/3] timer: Improve itimers scalability Hideaki Kimura <hideaki.kimura@hpe.com> - 2015-08-27 01:20 +0200
            Re: [PATCH 0/3] timer: Improve itimers scalability Frederic Weisbecker <fweisbec@gmail.com> - 2015-08-27 01:20 +0200
              Re: [PATCH 0/3] timer: Improve itimers scalability Hideaki Kimura <hideaki.kimura@hpe.com> - 2015-08-27 02:00 +0200
                Re: [PATCH 0/3] timer: Improve itimers scalability Frederic Weisbecker <fweisbec@gmail.com> - 2015-08-27 15:20 +0200
                Re: [PATCH 0/3] timer: Improve itimers scalability Steven Rostedt <rostedt@goodmis.org> - 2015-08-27 16:50 +0200
                Re: [PATCH 0/3] timer: Improve itimers scalability Thomas Gleixner <tglx@linutronix.de> - 2015-08-27 17:20 +0200
                Re: [PATCH 0/3] timer: Improve itimers scalability Frederic Weisbecker <fweisbec@gmail.com> - 2015-08-27 17:20 +0200

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