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SubjectRe: [PATCH] sched: Accelerate "pick_next_entity" under special condition
Hi, peter

Thanks so much for your reply :)

On 01/16/2012 05:51 PM, Peter Zijlstra wrote:

> On Mon, 2012-01-16 at 17:37 +0800, Michael Wang wrote:
>> From: Michael Wang <wangyun@linux.vnet.ibm.com>
>>
>> We can avoid some useless operation in some special condition.
>
> This is a pretty empty statement.
>
>> For example:
>> If we have "cfs_rq->next" and it can be use, we just return it directly.
>
> What it doesn't state is what it actually does, if it affects the common
> case and performance numbers (or a good reason for the lack thereof).
>


Please help me to understand the logic, I think in the original code,
even if we have cfs_rq->next and wakeup_preempt_entity check passed, we
still need to do a lot of work (check cfs_rq->last for example) which
have no influence on result, will it be better if we skip them and just
do what really needed?

>> Signed-off-by: Michael Wang <wangyun@linux.vnet.ibm.com>
>> ---
>> kernel/sched/fair.c | 28 +++++++++++++++++-----------
>> 1 files changed, 17 insertions(+), 11 deletions(-)
>>
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index 84adb2d..9fc2c3c 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -1295,6 +1295,8 @@ set_next_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
>> static int
>> wakeup_preempt_entity(struct sched_entity *curr, struct sched_entity *se);
>>
>> +#define ENTITY_PREEMPT_ALLOWED(prev,next) (wakeup_preempt_entity(prev, next) < 1)
>

> This is just uglification imo, its shouting and it doesn't actually win
> you much space.
>


I see, sorry for the bad idea.

Best regards,
Michael Wang



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