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

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Message-ID: <20140619204220.GJ4904@linux.vnet.ibm.com>
Date:	Thu, 19 Jun 2014 13:42:20 -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 03:31:56PM -0500, Christoph Lameter wrote:
> On Thu, 19 Jun 2014, Paul E. McKenney wrote:
> 
> > That is a separate issue, but unnecessary calls to cond_resched()
> > should of course be removed -- no argument there.
> 
> It looks like we are fighting higher latencies by adding calls in most of
> the critical sections which will in turn increase the latencies that we
> are trying to reduce.

That is on battle in a larger war.  Another battle is to keep big systems
from choking and dying.  We need to win both battles, though I understand
that you are focused primarily on latency reduction.  I don't get that
luxury because RCU is used across the board.

							Thanx, Paul

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