linux-kernel - Re: [Resend PATCH V2] X86/CPU: Avoid 100ms sleep for cpu offline during S3

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Date:	Wed, 24 Sep 2014 15:00:19 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Lan Tianyu <tianyu.lan@...el.com>
Cc:	tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
	x86@...nel.org, toshi.kani@...com, imammedo@...hat.com,
	bp@...en8.de, prarit@...hat.com,
	Peter Zijlstra <peterz@...radead.org>, srostedt@...hat.com,
	linux-kernel@...r.kernel.org
Subject: Re: [Resend PATCH V2] X86/CPU: Avoid 100ms sleep for cpu offline
 during S3


* Lan Tianyu <tianyu.lan@...el.com> wrote:

> On 2014年08月26日 15:43, Lan Tianyu wrote:
> > With some bad kernel configures, cpu offline consumes more than 100ms
> > during S3. This because native_cpu_die() would fall into 100ms
> > sleep when cpu idle loop thread marked cpu state to DEAD slower. It's
> > timing related issue. What native_cpu_die() does is that poll cpu
> > state and wait for 100ms if cpu state hasn't been marked to DEAD.
> > The 100ms sleep doesn't make sense. To avoid such long sleep, this
> > patch is to add struct completion to each cpu, wait for the completion
> > in the native_cpu_die() and wakeup the completion when the cpu state is
> > marked to DEAD.
> > 
> > Tested on the Intel Xeon server with 48 cores, Ivbridge and Haswell laptops.
> > the times of cpu offline on these machines are reduced from more than 100ms
> > to less than 5ms. The system suspend time reduces 2.3s on the servers.
> > 
> > Borislav and Prarit also helped to test the patch on an AMD machine and
> > a few systems of various sizes and configurations (multi-socket,
> > single-socket, no hyper threading, etc.). No issues seen.
> > 
> > Acked-by: Borislav Petkov <bp@...e.de>
> > Tested-by: Prarit Bhargava <prarit@...hat.com>
> > Signed-off-by: Lan Tianyu <tianyu.lan@...el.com>
> > ---
> >  arch/x86/kernel/smpboot.c | 23 +++++++++++------------
> >  1 file changed, 11 insertions(+), 12 deletions(-)
> > 
> 
> Hi HPA, Ingo, Thomas & Peter Z:
> 	Is this patch ok for you?

Nice patch!

I cleaned up a few small details and will push it out if it 
passes testing.

Thanks,

	Ingo
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