linux-kernel - Re: [PATCH 0/3] timer: Improve itimers scalability

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Date:	Wed, 26 Aug 2015 15:07:27 -0700
From:	Jason Low <jason.low2@...com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org,
	Frederic Weisbecker <fweisbec@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Rik van Riel <riel@...hat.com>,
	Scott J Norton <scott.norton@...com>, jason.low2@...com,
	hideaki.kimura@....com
Subject: Re: [PATCH 0/3] timer: Improve itimers scalability

On Wed, 2015-08-26 at 19:08 +0200, Oleg Nesterov wrote:
> On 08/26, Jason Low wrote:
> >
> > Hi Andrew,
> >
> > On Tue, 2015-08-25 at 20:27 -0700, Andrew Morton wrote:
> > > On Tue, 25 Aug 2015 20:17:45 -0700 Jason Low <jason.low2@...com> wrote:
> > >
> > > > When running a database workload on a 16 socket machine, there were
> > > > scalability issues related to itimers.
> > > >
> > > > Commit 1018016c706f addressed the issue with the thread_group_cputimer
> > > > spinlock taking up a significant portion of total run time.
> > > >
> > > > This patch series address the other issue where a lot of time is spent
> > > > trying to acquire the sighand lock. It was found in some cases that
> > > > 200+ threads were simultaneously contending for the same sighand lock,
> > > > reducing throughput by more than 30%.
> > >
> > > Does this imply that the patchset increased the throughput of this
> > > workload by 30%?
> > >
> > > And is this test case realistic?  If not, what are the benefits on a
> > > real-world workload?
> >
> > Yes, the test case with the database workload is realistic.
> 
> Can't resists, sorry... to me the very idea to use the process wide posix-
> cpu-timers on performance critical application doesn't look realistic ;)

I will let Hideaki elaborate more regarding the issue at the application
level.

> However, I thinks the patches are fine.
> 
> 
> Reviewed-by: Oleg Nesterov <oleg@...hat.com>

Thanks for reviewing!

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