[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <20070305023534.GB16666@wotan.suse.de>
Date: Mon, 5 Mar 2007 03:35:34 +0100
From: Nick Piggin <npiggin@...e.de>
To: "Siddha, Suresh B" <suresh.b.siddha@...el.com>
Cc: akpm@...ux-foundation.org, mingo@...e.hu,
linux-kernel@...r.kernel.org
Subject: Re: [patch] sched: optimize siblings status check logic in wake_idle()
On Fri, Mar 02, 2007 at 08:23:32PM -0800, Suresh B wrote:
> When a logical cpu 'x' already has more than one process running, then most likely
> the siblings of that cpu 'x' must be busy. Otherwise the idle siblings
> would have likely(in most of the scenarios) picked up the extra load making
> the load on 'x' atmost one.
Do you have any stats on this?
> Use this logic to eliminate the siblings status check and minimize the cache
> misses encountered on a heavily loaded system.
Well it does increase the cacheline footprint a bit, but all cachelines
should be local to our L1 cache, presuming you don't have any CPUs where
threads have seperate caches.
What sort of numbers do you have?
>
> Signed-off-by: Suresh Siddha <suresh.b.siddha@...el.com>
> ---
>
> diff --git a/kernel/sched.c b/kernel/sched.c
> index 0dc7572..d1ecc56 100644
> --- a/kernel/sched.c
> +++ b/kernel/sched.c
> @@ -1368,7 +1368,16 @@ static int wake_idle(int cpu, struct task_struct *p)
> struct sched_domain *sd;
> int i;
>
> - if (idle_cpu(cpu))
> + /*
> + * If it is idle, then it is the best cpu to run this task.
> + *
> + * This cpu is also the best, if it has more than one task already.
> + * Siblings must be also busy(in most cases) as they didn't already
> + * pickup the extra load from this cpu and hence we need not check
> + * sibling runqueue info. This will avoid the checks and cache miss
> + * penalities associated with that.
> + */
> + if (idle_cpu(cpu) || cpu_rq(cpu)->nr_running > 1)
> return cpu;
>
> for_each_domain(cpu, sd) {
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists