From: Robin Holt <holt@sgi.com>
To: Russ Anderson <rja@sgi.com>
Cc: "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>,
Paul Mackerras <paulus@samba.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Ingo Molnar <mingo@kernel.org>, Robin Holt <holt@sgi.com>,
"H. Peter Anvin" <hpa@zytor.com>,
Andrew Morton <akpm@linux-foundation.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Shawn Guo <shawn.guo@linaro.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>,
the arch/x86 maintainers <x86@kernel.org>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Tejun Heo <tj@kernel.org>, Oleg Nesterov <oleg@redhat.com>,
Lai Jiangshan <laijs@cn.fujitsu.com>,
Michel Lespinasse <walken@google.com>,
"rusty@rustcorp.com.au" <rusty@rustcorp.com.au>,
Peter Zijlstra <peterz@infradead.org>
Subject: Re: Bulk CPU Hotplug (Was Re: [PATCH] Do not force shutdown/reboot to boot cpu.)
Date: Thu, 11 Apr 2013 16:08:55 -0500 [thread overview]
Message-ID: <20130411210855.GJ3658@sgi.com> (raw)
In-Reply-To: <20130411200820.GA10167@sgi.com>
On Thu, Apr 11, 2013 at 03:08:20PM -0500, Russ Anderson wrote:
> On Thu, Apr 11, 2013 at 08:15:27PM +0530, Srivatsa S. Bhat wrote:
> > On 04/11/2013 07:53 PM, Russ Anderson wrote:
> > > On Thu, Apr 11, 2013 at 06:15:18PM +0530, Srivatsa S. Bhat wrote:
> > >>
> > >> One more thing we have to note is that, there are 4 notifiers for taking a
> > >> CPU offline:
> > >>
> > >> CPU_DOWN_PREPARE
> > >> CPU_DYING
> > >> CPU_DEAD
> > >> CPU_POST_DEAD
> > >>
> > >> The first can be run in parallel as mentioned above. The second is run in
> > >> parallel in the stop_machine() phase as shown in Russ' patch. But the third
> > >> and fourth set of notifications all end up running only on CPU0, which will
> > >> again slow down things.
> > >
> > > In my testing the third and fourth set were a small part of the overall
> > > time. Less than 10%, with cpu notifiers 90+% of the time.
> >
> > *All* of them are cpu notifiers! All of them invoke __cpu_notify() internally.
> > So how did you differentiate between them and find out that the third and
> > fourth sets take less time?
>
> I reran a test on a 1024 cpu system, using my test patch to only call
> __stop_machine() once. Added printks to show the kernel timestamp
> at various points.
>
> When calling disable_nonboot_cpus() and enable_nonboot_cpus() just after
> booting the system:
> The loop calling __cpu_notify(CPU_DOWN_PREPARE) took 376.6 seconds.
> The loop calling cpu_notify_nofail(CPU_DEAD) took 8.1 seconds.
>
> My guess is that notifiers do more work in the CPU_DOWN_PREPARE case.
>
> I also added a loop calling a new notifier (CPU_TEST) which none of
> notifiers would recognize, to measure the time it took to spin through
> the call chain without the notifiers doing any work. It took
> 0.0067 seconds.
>
> On the actual reboot, as the system was shutting down:
> The loop calling __cpu_notify(CPU_DOWN_PREPARE) took 333.8 seconds.
> The loop calling cpu_notify_nofail(CPU_DEAD) took 2.7 seconds.
How about if you take the notifier_call_chain function copy it
to kernel/sys.c, and time each notifier_call() callout individually.
Robin
next prev parent reply other threads:[~2013-04-11 21:09 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-04-03 19:37 [PATCH] Do not force shutdown/reboot to boot cpu Robin Holt
2013-04-08 15:57 ` Ingo Molnar
2013-04-08 16:11 ` H. Peter Anvin
2013-04-08 16:59 ` Robin Holt
2013-04-10 11:16 ` Ingo Molnar
2013-04-10 14:01 ` Robin Holt
2013-04-10 15:10 ` Linus Torvalds
2013-04-10 15:29 ` Russ Anderson
2013-04-10 16:59 ` Ingo Molnar
2013-04-10 17:14 ` Robin Holt
2013-04-10 17:22 ` Ingo Molnar
2013-04-10 17:55 ` Robin Holt
2013-04-10 19:00 ` Robin Holt
2013-04-11 8:57 ` Ingo Molnar
2013-04-11 11:34 ` Robin Holt
2013-04-11 12:00 ` Ingo Molnar
2013-04-11 12:03 ` Robin Holt
2013-04-11 12:08 ` Robin Holt
2013-04-11 12:14 ` Ingo Molnar
2013-04-10 17:58 ` H. Peter Anvin
2013-04-10 23:02 ` Russ Anderson
2013-04-10 22:29 ` Russ Anderson
2013-04-11 5:31 ` Paul Mackerras
2013-04-11 12:45 ` Bulk CPU Hotplug (Was Re: [PATCH] Do not force shutdown/reboot to boot cpu.) Srivatsa S. Bhat
2013-04-11 13:48 ` Robin Holt
2013-04-12 5:37 ` Ingo Molnar
2013-04-12 6:09 ` Srivatsa S. Bhat
2013-04-12 9:31 ` Robin Holt
2013-04-12 10:01 ` Robin Holt
2013-04-13 16:30 ` Oleg Nesterov
2013-04-15 16:04 ` Robin Holt
2013-04-15 16:09 ` Oleg Nesterov
2013-04-15 16:10 ` Robin Holt
2013-04-13 17:01 ` Srivatsa S. Bhat
2013-04-15 10:16 ` Ingo Molnar
2013-04-15 12:02 ` Robin Holt
2013-04-15 15:59 ` Robin Holt
2013-04-16 9:40 ` Ingo Molnar
2013-04-11 14:23 ` Russ Anderson
2013-04-11 14:45 ` Srivatsa S. Bhat
2013-04-11 20:08 ` Russ Anderson
2013-04-11 20:17 ` Srivatsa S. Bhat
2013-04-11 21:08 ` Robin Holt [this message]
2013-04-08 16:54 ` [PATCH] Do not force shutdown/reboot to boot cpu Robin Holt
2013-04-08 17:07 ` Russ Anderson
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