linux-kernel - Re: sched: Performance of Trade workload running inside VM

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Message-ID: <20120220150943.GD2350@linux.vnet.ibm.com>
Date:	Mon, 20 Feb 2012 20:39:48 +0530
From:	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	mingo@...e.hu, pjt@...gle.com, efault@....de, venki@...gle.com,
	suresh.b.siddha@...el.com, linux-kernel@...r.kernel.org,
	"Nikunj A. Dadhania" <nikunj@...ux.vnet.ibm.com>
Subject: Re: sched: Performance of Trade workload running inside VM

* Peter Zijlstra <a.p.zijlstra@...llo.nl> [2012-02-20 15:56:30]:

> > Another variant of the patch could be to have select_idle_sibling() look
> > for any idle cpu that is in same cache domain (rather than looking for a
> > whole group of cpus to be idle)?
> 
> Right, so I looked over select_idle_sibling() again and it made my head
> hurt :/

I can vouch for it :-)

> I can't immediately tell if its actually doing the right thing
> or not (it _should_ try and avoid using SMT siblings if possible).

Yes makes sense.

> It would be very nice not to have both select_idle_sibling() and
> SD_BALANCE_WAKE iterate the domain tree. So merging them if at all
> possible would be goodness I think.

Right. Let me see how that can be worked out in my next version.

> We'd have WAKE_AFFINE to decide which cache domain etc to stuff the task
> on and then use select_idle_sibling() to find the most appropriate cpu
> within that cache domain.
> 
> There was talk of modifying select_idle_sibling() to also consider the
> C-state the cpu was in, preferring shallower over deeper C-states where
> there's choice,

Ok ..interesting. /me goes and educates himself how this info can be dug
out.

> this is very similar to what you propose, taking the
> least loaded cpu when there isn't a proper idle one around.

Thanks for the feedback ..

- vatsa

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