linux-kernel - Re: [RFCv3 PATCH 33/48] sched: Energy-aware wake-up task placement

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20150324154242.GG18994@e105550-lin.cambridge.arm.com>
Date:	Tue, 24 Mar 2015 15:42:42 +0000
From:	Morten Rasmussen <morten.rasmussen@....com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	"mingo@...hat.com" <mingo@...hat.com>,
	"vincent.guittot@...aro.org" <vincent.guittot@...aro.org>,
	Dietmar Eggemann <Dietmar.Eggemann@....com>,
	"yuyang.du@...el.com" <yuyang.du@...el.com>,
	"preeti@...ux.vnet.ibm.com" <preeti@...ux.vnet.ibm.com>,
	"mturquette@...aro.org" <mturquette@...aro.org>,
	"nico@...aro.org" <nico@...aro.org>,
	"rjw@...ysocki.net" <rjw@...ysocki.net>,
	Juri Lelli <Juri.Lelli@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFCv3 PATCH 33/48] sched: Energy-aware wake-up task placement

On Tue, Mar 24, 2015 at 01:00:58PM +0000, Peter Zijlstra wrote:
> On Wed, Feb 04, 2015 at 06:31:10PM +0000, Morten Rasmussen wrote:
> > @@ -5138,6 +5224,10 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_f
> >  		prev_cpu = cpu;
> >  
> >  	if (sd_flag & SD_BALANCE_WAKE) {
> > +		if (energy_aware()) {
> > +			new_cpu = energy_aware_wake_cpu(p);
> > +			goto unlock;
> > +		}
> >  		new_cpu = select_idle_sibling(p, prev_cpu);
> >  		goto unlock;
> >  	}
> 
> So that is fundamentally wrong I think. We only care about power aware
> scheduling when U < 1, after that we should do the normal thing. This
> setup does not allow for that.

Right, I agree that we should preferably do the normal thing for U ~= 1.
We can restructure the wake-up path to follow that pattern, but we need
to know U beforehand to choose the right path. U isn't just
get_cpu_usage(prev_cpu) but some broader view of the of the cpu
utilizations. For example, prev_cpu might be full, but everyone else is
idle so we still want to try to do an energy aware wake-up on some other
cpu. U could be the minium utilization of all cpus in prev_cpu's
sd_llc, which is somewhat similar to what energy_aware_wake_cpu() does.

I guess energy_aware_wake_cpu() could be refactored to call
select_idle_sibling() if it find U ~= 1?
--
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/