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posix_cpu_timer: Check thread timers only when there are active thread timers 

The fastpath_timer_check() contains logic to check for if any timers
are set by checking if !task_cputime_zero(). Similarly, we can do this
before calling check_thread_timers(). In the case where there
are only process-wide timers, this will skip all of the computations for
per-thread timers when there are no per-thread timers.

As suggested by George, we can put the task_cputime_zero() check in
check_thread_timers(), since that is more of an optization to the
function. Similarly, we move the existing check of cputimer->running
to check_process_timers().

Signed-off-by: Jason Low <jason.low2@hp.com>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: George Spelvin <linux@horizon.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: hideaki.kimura@hpe.com
Cc: terry.rudd@hpe.com
Cc: scott.norton@hpe.com
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1444849677-29330-3-git-send-email-jason.low2@hp.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Jason Low 2015-10-14 12:07:54 -07:00 committed by Thomas Gleixner
parent 7c177d994e
commit 934715a191
1 changed files with 16 additions and 6 deletions
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22
kernel/time/posix-cpu-timers.c
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@ -864,6 +864,13 @@ static void check_thread_timers(struct task_struct *tsk,
unsigned long long expires;
unsigned long soft;
/*
* If cputime_expires is zero, then there are no active
* per thread CPU timers.
*/
if (task_cputime_zero(&tsk->cputime_expires))
return;
expires = check_timers_list(timers, firing, prof_ticks(tsk));
tsk_expires->prof_exp = expires_to_cputime(expires);
@ -961,6 +968,13 @@ static void check_process_timers(struct task_struct *tsk,
struct task_cputime cputime;
unsigned long soft;
/*
* If cputimer is not running, then there are no active
* process wide timers (POSIX 1.b, itimers, RLIMIT_CPU).
*/
if (!READ_ONCE(tsk->signal->cputimer.running))
return;
/*
* Collect the current process totals.
*/
@ -1169,12 +1183,8 @@ void run_posix_cpu_timers(struct task_struct *tsk)
* put them on the firing list.
*/
check_thread_timers(tsk, &firing);
/*
* If there are any active process wide timers (POSIX 1.b, itimers,
* RLIMIT_CPU) cputimer must be running.
*/
if (READ_ONCE(tsk->signal->cputimer.running))
check_process_timers(tsk, &firing);
check_process_timers(tsk, &firing);
/*
* We must release these locks before taking any timer's lock.