Messages in this thread | | | Subject | Re: [PATCH RFC] reduce runqueue lock contention | From | Peter Zijlstra <> | Date | Thu, 20 May 2010 23:09:46 +0200 |
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On Thu, 2010-05-20 at 16:48 -0400, Chris Mason wrote: > > This is more of a starting point than a patch, but it is something I've > been meaning to look at for a long time. Many different workloads end > up hammering very hard on try_to_wake_up, to the point where the > runqueue locks dominate CPU profiles.
Right, so one of the things that I considered was to make p->state an atomic_t and replace the initial stage of try_to_wake_up() with something like:
int try_to_wake_up(struct task *p, unsigned int mask, wake_flags) { int state = atomic_read(&p->state);
do { if (!(state & mask)) return 0;
state = atomic_cmpxchg(&p->state, state, TASK_WAKING); } while (state != TASK_WAKING);
/* do this pending queue + ipi thing */
return 1; }
Also, I think we might want to put that atomic single linked list thing into some header (using atomic_long_t or so), because I have a similar thing living in kernel/perf_event.c, that needs to queue things from NMI context.
The advantage of doing basically the whole enqueue on the remote cpu is less cacheline bouncing of the runqueue structures.
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