linux-kernel - Re: [PATCH v7 0/8] Tunable sched_mc_power

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Date:	Tue, 06 Jan 2009 10:31:37 +0100
From:	Mike Galbraith <efault@....de>
To:	svaidy@...ux.vnet.ibm.com
Cc:	Ingo Molnar <mingo@...e.hu>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v7 0/8] Tunable sched_mc_power_savings=n

On Mon, 2009-01-05 at 16:19 +0100, Mike Galbraith wrote:
> On Mon, 2009-01-05 at 07:37 +0100, Mike Galbraith wrote:
> 
> > I'll rummage around.
> 
> Seems to be about the only thing it could be, load balancing inflicting
> injury on very sensitive mysql+oltp pairs.

BTW, I verified this.  Reverting all load-balancing changes fully
restored mysql+oltp peak, and brought mid-range throughput to the same
level as sched_mc=2 except at the log-jam end.  (haven't looked at
vmark, though I'd expect it to be hurting a bit too, it's affinity
sensitive as well)

I expected sched_mc=2 to help an nfs mount kbuild, and it did, quite a
bit.  I first tried an nfs4 mount, but after a while, the odd ipv6 80%
idle problem came back, so I reverted to nfs3.  Full built time there
went from 4m25s to 4m2s.  A nice improvement.

I haven't noticed anything on the interactivity front.

Personally, I'd go for sched_mc=2 as default.  I value the fork/exec
load much more than sensitive benchmarks, though what hurts mysql+oltp
will certainly hurt others as well.  We have a bit of conflict between
keeping CPUs busy and affinity cost.  Something to work on.

	-Mike

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