Messages in this thread | | | Date | Wed, 1 May 2013 13:00:47 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH 09/10] sched: task_sched_runtime introduce micro optimization |
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On Mon, Apr 29, 2013 at 11:17:17PM -0400, kosaki.motohiro@gmail.com wrote: > From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> > > rq lock in task_sched_runtime() is necessary for two reasons. 1) > accessing se.sum_exec_runtime is inatomic on 32bit and 2) > do_task_delta_exec() require it. > > And then, 64bit can avoid holds rq lock when add_delta is false. > > Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> > --- > kernel/sched/core.c | 6 ++++++ > 1 files changed, 6 insertions(+), 0 deletions(-) > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index b817e6d..24ba1c6 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -2657,6 +2657,12 @@ unsigned long long task_sched_runtime(struct task_struct *p, bool add_delta) > struct rq *rq; > u64 ns = 0; > > + /* Micro optimization. */
Instead of the above; how about something like:
/* 64-bit doesn't need locks to atomically read a 64bit value */
> +#ifdef CONFIG_64BIT > + if (!add_delta) > + return p->se.sum_exec_runtime; > +#endif > + > rq = task_rq_lock(p, &flags); > ns = p->se.sum_exec_runtime; > if (add_delta) > -- > 1.7.1 >
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