From: Russ Anderson <rja@sgi.com>
To: Ingo Molnar <mingo@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.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>
Subject: Re: [PATCH] Do not force shutdown/reboot to boot cpu.
Date: Wed, 10 Apr 2013 18:02:35 -0500 [thread overview]
Message-ID: <20130410230234.GB8112@sgi.com> (raw)
In-Reply-To: <20130410165934.GB21951@gmail.com>
On Wed, Apr 10, 2013 at 06:59:34PM +0200, Ingo Molnar wrote:
> * Russ Anderson <rja@sgi.com> wrote:
>
> > Yes, I have a test patch that replaces for_each_online_cpu(cpu) with a cpu
> > bitmask in disable_nonboot_cpus(). The lower level routines already take a
> > bitmask. It allows __stop_machine() to be called just once. That change
> > reduces shutdown time on a 1024 cpu machine from 16 minutes 4 minutes.
> > Significant improvement, but not good enough.
> >
> > The next significant bottleneck is __cpu_notify(). Tried creating worker
> > threads to parallelize the shutdown, but the problem is __cpu_notify() is not
> > thread safe. Putting a lock around it caused all the worker threads to fight
> > over the lock.
>
> 4 minutes bootup is 240 seconds, with 1024 CPUs that's about 240 msecs per CPU.
>
> That sounds a lot, given that unlike bootup there's not much real work to be done
> during shutdown - we don't initialize anything, etc.
>
> Maybe much of those 240 msecs are spent in some stupid udelay loop or so, which
> could be made parallel?
I was hoping for a stupid udelay when I first started looking
at this code, but found nothing obvious.
The bulk of the time (after making the cpu bitmask change) is
spent in __cpu_notify(), as explained above.
> Would it be possible to create a 'reboot but stop at the end and reactivate all
> CPUs again' reboot flag, so that it can all be NMI-profiled, to see where the true
> bottleneck is? A naked disable_nonboot_cpus() call in essence.
My testing was similar. I hacked a kernel module to call
disable_nonboot_cpus() and enable_nonboot_cpus() and used
printks to narrow down the slow functions. That points
at the cpu notifier call chain. It's not clear if any
of the functions on the call chain take a long time, or
just going sequentially through the list for all cpus just
takes a long time.
--
Russ Anderson, OS RAS/Partitioning Project Lead
SGI - Silicon Graphics Inc rja@sgi.com
next prev parent reply other threads:[~2013-04-10 23:02 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 [this message]
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
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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