linux-kernel - Re: UDP-U stream performance regression on 32-rc1 kernel

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Message-ID: <20091103174531.GA14747@elte.hu>
Date:	Tue, 3 Nov 2009 18:45:31 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>
Cc:	alex.shi@...el.com, linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Mike Galbraith <efault@....de>
Subject: Re: UDP-U stream performance regression on 32-rc1 kernel


* Zhang, Yanmin <yanmin_zhang@...ux.intel.com> wrote:

> On Tue, 2009-11-03 at 11:47 +0800, Alex Shi wrote:
> > We found the UDP-U 1k/4k stream of netperf benchmark have some
> > performance regression from 10% to 20% on our Tulsa and some NHM
> > machines. 
>  perf events shows function find_busiest_group consumes about 4.5% cpu 
> time with the patch while it only consumes 0.5% cpu time without the 
> patch.
> 
> The communication between netperf client and netserver is very fast. 
> When netserver receives a message and there is no new message 
> available, it goes to sleep and scheduler calls idle_balance => 
> load_balance_newidle. load_balance_newidle spends too much time and a 
> new message arrives quickly before load_balance_newidle ends.
> 
> As the comments in the patch say hackbench benefits from it, I tested 
> hackbench on Nehalem and core2 machines. hackbench does benefit from 
> it, about 6% on nehalem machines, but doesn't benefit on core2 
> machines.

Can you confirm that -tip:

  http://people.redhat.com/mingo/tip.git/README

has it fixed (or at least improved)?

	Ingo
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