linux-kernel - Re: sched: Avoid SMT siblings in select_idle

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Date:	Tue, 6 Mar 2012 10:14:11 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Mike Galbraith <efault@....de>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Paul Turner <pjt@...gle.com>
Subject: Re: sched: Avoid SMT siblings in select_idle_sibling() if possible


* Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com> wrote:

> * Peter Zijlstra <peterz@...radead.org> [2012-02-20 20:07:46]:
> 
> > On Mon, 2012-02-20 at 19:14 +0100, Mike Galbraith wrote:

> > > Enabling SD_BALANCE_WAKE used to be decidedly too 
> > > expensive to consider. Maybe that has changed, but I doubt 
> > > it.
> > 
> > Right, I through I remembered somet such, you could see it 
> > on wakeup heavy things like pipe-bench and that java msg 
> > passing thing, right?
> 
> I did some experiments with volanomark and it does turn out to 
> be sensitive to SD_BALANCE_WAKE, while the other wake-heavy 
> benchmark that I am dealing with (Trade) benefits from it.

Does volanomark still do yield(), thereby invoking a random 
shuffle of thread scheduling and pretty much voluntarily 
ejecting itself from most scheduler performance considerations?

If it uses a real locking primitive such as futexes then its 
performance matters more.

Thanks,

	Ingo
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