linux-kernel - Re: [bisected] pre-3.16 regression on open() scalability

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Message-ID: <alpine.DEB.2.11.1406190941180.2785@gentwo.org>
Date:	Thu, 19 Jun 2014 09:42:18 -0500 (CDT)
From:	Christoph Lameter <cl@...two.org>
To:	Andi Kleen <ak@...ux.intel.com>
cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Dave Hansen <dave.hansen@...el.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Josh Triplett <josh@...htriplett.org>,
	"Chen, Tim C" <tim.c.chen@...el.com>
Subject: Re: [bisected] pre-3.16 regression on open() scalability

On Wed, 18 Jun 2014, Andi Kleen wrote:

> I still think it's totally the wrong direction to pollute so
> many fast paths with this obscure debugging check workaround
> unconditionally.
>
> cond_resched() is in EVERY sleeping lock and in EVERY memory allocation!
> And these are really critical paths for many workloads.
>
> If you really wanted to do this I think you would first need
> to define a cond_resched_i_am_not_fast() or somesuch.
>
> Or put it all behind some debugging ifdef.

Again I am fully on Andi's side here. Please remove these frequent calls
to cond_resched. If one wants a fully preemptable kernel then please use
CONFIG_PREEMPT.

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