lkml.org 
[lkml]   [2014]   [May]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [RFC][PATCH 0/8] sched,idle: need resched polling rework
On Thu, May 22, 2014 at 02:58:18PM +0200, Peter Zijlstra wrote:
> ---
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 4ea7b3f1a087..a5da85fb3570 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -546,12 +546,38 @@ static bool set_nr_and_not_polling(struct task_struct *p)
> struct thread_info *ti = task_thread_info(p);
> return !(fetch_or(&ti->flags, _TIF_NEED_RESCHED) & _TIF_POLLING_NRFLAG);
> }
> +
> +/*
> + * Atomically set TIF_NEED_RESCHED if TIF_POLLING_NRFLAG is set.
> + */
> +static bool set_nr_if_polling(struct task_struct *p)
> +{
> + struct thread_info *ti = task_thread_info(p);
> + typeof(ti->flags) old, val = ti->flags;
> +
> + for (;;) {
> + if (!(val & _TIF_POLLING_NRFLAG))
> + return false;
> + if (val & _TIF_NEED_RESCHED)
> + return true;

Hmm, I think this is racy, false would be safer. If its already set we
might already be past the sched_ttwu_pending() invocation, while if its
clear and we're the one to set it, we're guaranteed not.

> + old = cmpxchg(&ti->flags, val, val | _TIF_NEED_RESCHED);
> + if (old == val)
> + return true;
> + val = old;
> + }
> +}
[unhandled content-type:application/pgp-signature]
\
 
 \ /
  Last update: 2014-05-22 15:41    [W:0.109 / U:0.440 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site