linux-kernel - Re: hackbench regression with kernel 2.6.32-rc1

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Message-Id: <1256654547.17752.13.camel@marge.simson.net>
Date:	Tue, 27 Oct 2009 15:42:27 +0100
From:	Mike Galbraith <efault@....de>
To:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>
Subject: Re: hackbench regression with kernel 2.6.32-rc1

On Tue, 2009-10-27 at 16:03 +0800, Zhang, Yanmin wrote:
> On Fri, 2009-10-16 at 13:06 +0200, Mike Galbraith wrote:
> > On Tue, 2009-10-13 at 11:12 +0800, Zhang, Yanmin wrote:
> > 
> > > NEXT_BUDDY has no help on volanoMark and tbench.
> > 
> > Can you try the patch below please?  It does tries to preserve buddy
> > affinity where possible, and mitigates over-preemption by strengthening
> > buddies a bit.  It improves vmark here by ~7%.
> I ran some benchmarks against 2.6.32-rc1+Peter_2_patches+below_patch.
> Below result is against 2.6.32-rc1.
> hackbench result has about 10% improvement on stoakley (2*4 cores) and
> tigerton (4*4 cores).
> tbench still has about 5% regression on stoakley and tigerton.
> VolanoMark has 33% regression on tigerton, but has 2% improvement on stoakley.
> 
> I also ran the benchmarks against the latest tips/master and got the similiar
> results like above testing.
> 
> The testing against tips on Nehalem machine didn't show much improvement/regression.

Thanks for the testing.  Your results suggest that I should revive the
mark buddies whether you use them or not idea.

	-Mike

 
> > diff --git a/kernel/sched.c b/kernel/sched.c
> > index 00f9e71..fb025d4 100644
> > --- a/kernel/sched.c
> > +++ b/kernel/sched.c
> > @@ -2007,8 +2007,12 @@ task_hot(struct task_struct *p, u64 now, struct sched_domain *sd)
> >  
> >  	/*
> >  	 * Buddy candidates are cache hot:
> > +	 *
> > +	 * Do not honor buddies if there may be nothing else to
> > +	 * prevent us from becoming idle.
> >  	 */
> >  	if (sched_feat(CACHE_HOT_BUDDY) &&
> > +			task_rq(p)->nr_running >= sched_nr_latency &&
> >  			(&p->se == cfs_rq_of(&p->se)->next ||
> >  			 &p->se == cfs_rq_of(&p->se)->last))
> >  		return 1;
> > diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
> > index c32c3e6..428bf55 100644
> > --- a/kernel/sched_fair.c
> > +++ b/kernel/sched_fair.c
> > @@ -863,18 +863,20 @@ static struct sched_entity *pick_next_entity(struct cfs_rq *cfs_rq)
> >  	struct sched_entity *se = __pick_next_entity(cfs_rq);
> >  	struct sched_entity *buddy;
> >  
> > -	if (cfs_rq->next) {
> > +	if (cfs_rq->next && sched_feat(NEXT_BUDDY)) {
> >  		buddy = cfs_rq->next;
> > -		cfs_rq->next = NULL;
> > -		if (wakeup_preempt_entity(buddy, se) < 1)
> > +		if (wakeup_preempt_entity(buddy, se) < 1) {
> > +			cfs_rq->next = NULL;
> >  			return buddy;
> > +		}
> >  	}
> >  
> > -	if (cfs_rq->last) {
> > +	if (cfs_rq->last && sched_feat(LAST_BUDDY)) {
> >  		buddy = cfs_rq->last;
> > -		cfs_rq->last = NULL;
> > -		if (wakeup_preempt_entity(buddy, se) < 1)
> > +		if (wakeup_preempt_entity(buddy, se) < 1) {
> > +			cfs_rq->last = NULL;
> >  			return buddy;
> > +		}
> >  	}
> >  
> >  	return se;
> > @@ -1600,9 +1602,9 @@ static void check_preempt_wakeup(struct rq *rq, struct task_struct *p, int wake_
> >  	 * Also, during early boot the idle thread is in the fair class, for
> >  	 * obvious reasons its a bad idea to schedule back to the idle thread.
> >  	 */
> > -	if (sched_feat(LAST_BUDDY) && likely(se->on_rq && curr != rq->idle))
> > +	if (!(wake_flags & WF_FORK) && likely(se->on_rq && curr != rq->idle))
> >  		set_last_buddy(se);
> > -	if (sched_feat(NEXT_BUDDY) && !(wake_flags & WF_FORK))
> > +	if (!(wake_flags & WF_FORK))
> >  		set_next_buddy(pse);
> >  
> >  	/*
> > 
> > 
> 
> --
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