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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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