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

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Message-ID: <20140619213203.GA16747@cloud>
Date:	Thu, 19 Jun 2014 14:32:03 -0700
From:	josh@...htriplett.org
To:	Christoph Lameter <cl@...two.org>
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Andi Kleen <ak@...ux.intel.com>,
	Dave Hansen <dave.hansen@...el.com>,
	LKML <linux-kernel@...r.kernel.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 04:16:34PM -0500, Christoph Lameter wrote:
> This looks very much like the CONFIG_PREEMPT problem in not so
> extreme form. Maybe we need to add another config option:
> 
> CONFIG_REALLY_REALLY_NO_PREEMPT
> 
> to get the fastest code possible and those cond_rescheds removed from the
> critical paths?
> 
> Or better
> 
> CONFIG_PREEMPT_HALF_WAY
> 
> to enable those cond_rescheds.

That much actually does seem quite reasonable: making cond_resched() do
non-trivial work ought to have a config option to disable it.
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