Message-ID: <1376031129.18997.43.camel@marge.simpson.net>
Subject: Re: [PATCH V3]hrtimer: Fix a performance regression by disable
 reprogramming in remove_hrtimer
From: Mike Galbraith <bitbucket@online.de>
To: "ethan.zhao" <ethan.kernel@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>, johlstei@codeaurora.org,
        Yinghai Lu <yinghai@kernel.org>, Jin Feng <joe.jin@oracle.com>
Date: Fri, 09 Aug 2013 08:52:09 +0200
In-Reply-To: <BBA29515-CD89-47C5-B155-B71A6F6632DC@gmail.com>
References: <1374955447-5051-1-git-send-email-ethan.kernel@gmail.com>
	 <alpine.DEB.2.02.1307291146060.4089@ionos.tec.linutronix.de>
	 <CABawtvP4oLuvHOS3prbbgPShXVziV_wTo7i6KCqJ9KkoVdz0ag@mail.gmail.com>
	 <20130730093519.GP3008@twins.programming.kicks-ass.net>
	 <1375774140.5412.9.camel@marge.simpson.net>
	 <BBA29515-CD89-47C5-B155-B71A6F6632DC@gmail.com>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: 8BIT
Mime-Version: 1.0
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1854
Lines: 45

On Thu, 2013-08-08 at 23:02 +0800, ethan.zhao wrote: 
> 在 2013-8-6，下午3:29，Mike Galbraith <bitbucket@online.de> 写道：
> 
> > +int sched_needs_cpu(int cpu)
> > +{
> > +	return  cpu_rq(cpu)->avg_idle < sysctl_sched_migration_cost;
> > +}
> > +
> > #else /* CONFIG_NO_HZ_COMMON */
> > 
> > static inline bool got_nohz_idle_kick(void)
> > --- a/kernel/time/tick-sched.c
> > +++ b/kernel/time/tick-sched.c
> > @@ -548,7 +548,7 @@ static ktime_t tick_nohz_stop_sched_tick
> > 		time_delta = timekeeping_max_deferment();
> > 	} while (read_seqretry(&jiffies_lock, seq));
> > 
> > -	if (rcu_needs_cpu(cpu, &rcu_delta_jiffies) ||
> > +	if (sched_needs_cpu(cpu) || rcu_needs_cpu(cpu, &rcu_delta_jiffies) ||
> > 	    arch_needs_cpu(cpu) || irq_work_needs_cpu()) {
> > 		next_jiffies = last_jiffies + 1;
> > 		delta_jiffies = 1;
> 
> If the performace regression was caused by too much expensive clock device reprogramming and too frequent entering /exiting of C-states…   this patch should work.
> except the following result is almost always false under 3.11-rc3 code.
> 
> > return  cpu_rq(cpu)->avg_idle < sysctl_sched_migration_cost;

On my E5620 box, avg_idle works fine.  Patchlet doesn't save as much as
it used to, thanks to Peter's patch now killing the worst of the pain,
but it does still does save cycles.  I have too much regression left to
say exactly what it can now save max, doesn't matter much either.

The pertinent numbers:

v3.11-rc4-27-ge4ef108    496.7 KHz      .858     1.030     throttle+peterz
v3.11-rc4-27-ge4ef108    440.7 KHz      .761     1.296     nothrottle+peterz

-Mike

--
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/