Subject: Re: hackbench regression with kernel 2.6.32-rc1
From: Mike Galbraith <efault@gmx.de>
To: "Zhang, Yanmin" <yanmin_zhang@linux.intel.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>,
       LKML <linux-kernel@vger.kernel.org>, Ingo Molnar <mingo@elte.hu>
In-Reply-To: <1256630584.16282.13.camel@ymzhang>
References: <1255079943.25078.23.camel@ymzhang>
	 <1255084986.8802.46.camel@laptop>  <1255331120.3684.43.camel@ymzhang>
	 <1255357264.10420.15.camel@twins>  <1255403522.3684.57.camel@ymzhang>
	 <1255691192.7029.13.camel@marge.simson.net>
	 <1256630584.16282.13.camel@ymzhang>
Content-Type: text/plain; charset="UTF-8"
Date: Tue, 27 Oct 2009 15:42:27 +0100
Message-Id: <1256654547.17752.13.camel@marge.simson.net>
Mime-Version: 1.0
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 3820
Lines: 101

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);
> >  
> >  	/*
> > 
> > 
> 
> --
> 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/

--
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/