linux-kernel - Re: [PATCH v2 0/4] timer: Improve itimers scalability

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Message-ID: <1445016853.2517.16.camel@j-VirtualBox>
Date:	Fri, 16 Oct 2015 10:34:13 -0700
From:	Jason Low <jason.low@....com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Jason Low <jason.low2@...com>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org, Oleg Nesterov <oleg@...hat.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Davidlohr Bueso <dave@...olabs.net>,
	Steven Rostedt <rostedt@...dmis.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	George Spelvin <linux@...izon.com>, hideaki.kimura@....com,
	terry.rudd@....com, scott.norton@....com
Subject: Re: [PATCH v2 0/4] timer: Improve itimers scalability

On Fri, 2015-10-16 at 09:12 +0200, Ingo Molnar wrote:
> * Jason Low <jason.low@....com> wrote:
> 
> > > > With this patch set (along with commit 1018016c706f mentioned above),
> > > > the performance hit of itimers almost completely goes away on the
> > > > 16 socket system.
> > > > 
> > > > Jason Low (4):
> > > >   timer: Optimize fastpath_timer_check()
> > > >   timer: Check thread timers only when there are active thread timers
> > > >   timer: Convert cputimer->running to bool
> > > >   timer: Reduce unnecessary sighand lock contention
> > > > 
> > > >  include/linux/init_task.h      |    3 +-
> > > >  include/linux/sched.h          |    9 ++++--
> > > >  kernel/fork.c                  |    2 +-
> > > >  kernel/time/posix-cpu-timers.c |   63 ++++++++++++++++++++++++++++-----------
> > > >  4 files changed, 54 insertions(+), 23 deletions(-)
> > > 
> > > Is there some itimers benchmark that can be used to measure the effects of these 
> > > changes?
> > 
> > Yes, we also wrote a micro benchmark which generates cache misses and measures 
> > the average cost of each cache miss (with itimers enabled). We used this while 
> > writing and testing patches, since it takes a bit longer to set up and run the 
> > database.
> 
> Mind posting it, so that people can stick it into a new 'perf bench timer' 
> subcommand, and/or reproduce your results with it?

Yes, sure. At the moment, this micro benchmark is written in C++ and
integrated with the database code. We can look into rewriting it into a
more general program so that it can be included in perf.

Thanks,
Jason

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