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

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Message-ID: <20140619205044.GX8178@tassilo.jf.intel.com>
Date:	Thu, 19 Jun 2014 13:50:44 -0700
From:	Andi Kleen <ak@...ux.intel.com>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	Christoph Lameter <cl@...two.org>,
	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 01:42:20PM -0700, Paul E. McKenney wrote:
> 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

If we really need cond_resched() now to stop systems from dying
we did a really poor job at designing Linux. I hope it's not true,
that would be really bad and point to some severe design problems
elsewhere.

-Andi

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