linux-kernel - Re: rcu: performance regression

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Message-ID: <1308057298.19856.40.camel@twins>
Date:	Tue, 14 Jun 2011 15:14:58 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	paulmck@...ux.vnet.ibm.com
Cc:	"Alex,Shi" <alex.shi@...el.com>,
	"Li, Shaohua" <shaohua.li@...el.com>, Ingo Molnar <mingo@...e.hu>,
	lkml <linux-kernel@...r.kernel.org>,
	"Chen, Tim C" <tim.c.chen@...el.com>, rostedt@...dmis.org
Subject: Re: rcu: performance regression

On Tue, 2011-06-14 at 06:02 -0700, Paul E. McKenney wrote:
> > This commit also cause hackbench process mode performance dropping, and
> > Shaohua's patch do recovered this. But in hackbench testing, the vmstat
> > show context switch have some reduce. And perf tool show
> > root_domain->cpupri->prio_to_cpu[]->lock has contention with the commit.
> 
> Steven, Peter, would any of the recent fixes address this lock contention? 

No. People occasionally run into that thing, but given the constraints
on SCHED_FIFO SMP (run the n highest priority tasks on m cpus; n<=m)
there isn't really much we can do.

IIRC Chris Mason once proposed a lockless version, but that opened up
race windows, Steve might know the details better.
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