Messages in this thread | | | Date | Mon, 5 Mar 2007 03:35:34 +0100 | From | Nick Piggin <> | Subject | Re: [patch] sched: optimize siblings status check logic in wake_idle() |
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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@intel.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@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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