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

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Message-ID: <20140805084135.GB18234@pd.tnic>
Date:	Tue, 5 Aug 2014 10:41:35 +0200
From:	Borislav Petkov <bp@...en8.de>
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,
	jan.kiszka@...mens.com, mingo@...nel.org, huawei.libin@...wei.com,
	prarit@...hat.com, linux-kernel@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] X86/CPU: Avoid 100ms sleep for cpu offline  during S3

On Mon, Aug 04, 2014 at 04:59:02PM +0800, Lan Tianyu wrote:
> Some test result shows cpu offline consumes more than 100ms during S3.
> After some researchs, found native_cpu_die() would fall into 100ms
> sleep if cpu idle loop thread marked cpu state slower. 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.
> 
> Signed-off-by: Lan Tianyu <tianyu.lan@...el.com>
> ---
>  arch/x86/kernel/smpboot.c | 26 ++++++++++++++------------
>  1 file changed, 14 insertions(+), 12 deletions(-)

...

> @@ -1339,18 +1342,16 @@ int native_cpu_disable(void)
>  void native_cpu_die(unsigned int cpu)
>  {
>  	/* We don't do anything here: idle task is faking death itself. */
> -	unsigned int i;
> +	wait_for_completion_timeout(&per_cpu(die_complete, cpu),
> +			msecs_to_jiffies(1000));

One more thing peterz suggested. Just do:

	wait_for_completion_timeout(&per_cpu(die_complete, cpu), HZ);

because HZ is the number of jiffies in a second. Which is what you want
here.

-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
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