linux-kernel - Re: [PATCH v8 08/10] sched: add SD_PREFER

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Date:	Tue, 4 Nov 2014 09:58:35 +0100
From:	Vincent Guittot <vincent.guittot@...aro.org>
To:	Wanpeng Li <kernellwp@...il.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	Morten Rasmussen <Morten.Rasmussen@....com>,
	Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	LAK <linux-arm-kernel@...ts.infradead.org>,
	Rik van Riel <riel@...hat.com>,
	Mike Galbraith <efault@....de>,
	Nicolas Pitre <nicolas.pitre@...aro.org>,
	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>
Subject: Re: [PATCH v8 08/10] sched: add SD_PREFER_SIBLING for SMT level

On 4 November 2014 04:21, Wanpeng Li <kernellwp@...il.com> wrote:
> Hi Vincent,
> On 14/10/31 下午4:47, Vincent Guittot wrote:
>>
>> Add the SD_PREFER_SIBLING flag for SMT level in order to ensure that
>> the scheduler will put at least 1 task per core.
>
>
> What's the behavior before this patch?

Before this patch, the capacity_factor was 1 at core level (whatever
the number of CPUs in the core) so the group that represents this core
was overloaded as soon as more than 1 task was running on this group.
So if a core has 2 tasks running in its group, it is seen as
overloaded and the scheduler will try to migrate 1 task on a group
that is idle

Regards,
Vincent

>
> Regards,
> Wanpeng Li
>
>
>>
>> Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
>> Reviewed-by: Preeti U. Murthy <preeti@...ux.vnet.ibm.com>
>> ---
>>   kernel/sched/core.c | 1 +
>>   1 file changed, 1 insertion(+)
>>
>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
>> index 37fb92c..731f2ad 100644
>> --- a/kernel/sched/core.c
>> +++ b/kernel/sched/core.c
>> @@ -6165,6 +6165,7 @@ sd_init(struct sched_domain_topology_level *tl, int
>> cpu)
>>          */
>>         if (sd->flags & SD_SHARE_CPUCAPACITY) {
>> +               sd->flags |= SD_PREFER_SIBLING;
>>                 sd->imbalance_pct = 110;
>>                 sd->smt_gain = 1178; /* ~15% */
>>
>
>
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