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

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Message-ID: <1403146219.5189.4.camel@marge.simpson.net>
Date:	Thu, 19 Jun 2014 04:50:19 +0200
From:	Mike Galbraith <umgwanakikbuti@...il.com>
To:	paulmck@...ux.vnet.ibm.com
Cc:	Andi Kleen <ak@...ux.intel.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>,
	Christoph Lameter <cl@...ux.com>
Subject: Re: [bisected] pre-3.16 regression on open() scalability

On Wed, 2014-06-18 at 19:13 -0700, Paul E. McKenney wrote: 
> On Wed, Jun 18, 2014 at 06:42:00PM -0700, 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.
> 
> OOM prevention should count for something, I would hope.
> 
> > 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.
> 
> My first thought was to put it behind CONFIG_NO_HZ_FULL, but everyone
> seems to be enabling that one.

Not everybody, SUSE doesn't even have it enabled in factory.

-Mike

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