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

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Message-ID: <20150826170851.GA5264@redhat.com>
Date:	Wed, 26 Aug 2015 19:08:52 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Jason Low <jason.low2@...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>,
	Davidlohr Bueso <dave@...olabs.net>,
	Steven Rostedt <rostedt@...dmis.org>,
	Terry Rudd <terry.rudd@...com>, Rik van Riel <riel@...hat.com>,
	Scott J Norton <scott.norton@...com>
Subject: Re: [PATCH 0/3] timer: Improve itimers scalability

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 ;)

However, I thinks the patches are fine.


Reviewed-by: Oleg Nesterov <oleg@...hat.com>

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