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

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Message-ID: <20140619230732.GX4904@linux.vnet.ibm.com>
Date:	Thu, 19 Jun 2014 16:07:32 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	josh@...htriplett.org
Cc:	Christoph Lameter <cl@...two.org>, 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 02:32:03PM -0700, josh@...htriplett.org wrote:
> 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.

I am putting together patches based on Eric Dumazet's suggestion and on a
variant of the above approach.  However, I do expect the distros to starve
to death between those two bales of hay.  But perhaps the actual patches
will inspire a bit of light to go with this thread's heat and smoke.

							Thanx, Paul

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