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

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Date:	Thu, 19 Jun 2014 11:09:16 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Christoph Lameter <cl@...two.org>
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>
Subject: Re: [bisected] pre-3.16 regression on open() scalability

On Thu, Jun 19, 2014 at 09:42:18AM -0500, Christoph Lameter wrote:
> 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.

That is a separate issue, but unnecessary calls to cond_resched()
should of course be removed -- no argument there.

							Thanx, Paul

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