linux-kernel - Re: [RFC PATCH] sched: let task migration destination cpu do active balance

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Thu, 17 Apr 2014 13:42:48 +0800
From:	Alex Shi <alex.shi@...aro.org>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	mingo@...hat.com, morten.rasmussen@....com,
	vincent.guittot@...aro.org, daniel.lezcano@...aro.org,
	efault@....de, chris.redpath@....com, wangyun@...ux.vnet.ibm.com,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] sched: let task migration destination cpu do active
 balance

On 04/16/2014 08:13 PM, Peter Zijlstra wrote:
> On Wed, Apr 16, 2014 at 07:34:29PM +0800, Alex Shi wrote:
>> Chris Redpath found an issue on active balance: 
>> We let the task source cpu, the busiest cpu, do the active balance,
>> while the destination cpu maybe idle. thus we take the busiest cpu
>> time, but left the idlest cpu wait. That is not good for performance.
>>
>> This patch let the destination cpu do active balance. It will give tasks
>> more running time.
>>
>> Signed-off-by: Alex Shi <alex.shi@...aro.org>
>> ---
>>  kernel/sched/fair.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index 9b4c4f3..cccee76 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -6308,7 +6308,7 @@ more_balance:
>>  			raw_spin_unlock_irqrestore(&busiest->lock, flags);
>>  
>>  			if (active_balance) {
>> -				stop_one_cpu_nowait(cpu_of(busiest),
>> +				stop_one_cpu_nowait(busiest->push_cpu,
>>  					active_load_balance_cpu_stop, busiest,
>>  					&busiest->active_balance_work);
>>  			}
> 
> This doesn't make sense, the whole point of active balance is that we're
> going to move current, for that to work we have to interrupt the CPU
> current is running on and make sure another task (the stopper task in
> this case) is running, so that the previous current is now a !running
> task and we can move it around.
> 

Sure, you are right. thanks for correction!

-- 
Thanks
    Alex
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/