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

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Date:	Tue, 05 Aug 2014 17:28:52 +0800
From:	Lan Tianyu <tianyu.lan@...el.com>
To:	Borislav Petkov <bp@...en8.de>
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 2014年08月05日 16:41, Borislav Petkov wrote:
> 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.
> 

Yes, that looks better. I will update.


-- 
Best regards
Tianyu Lan
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