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....@linaro.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
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