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sched/fair: Explain why MIN_SHARES isn't scaled in calc_cfs_shares() 

Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Turner <pjt@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Samuel Thibault <samuel.thibault@ens-lyon.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/e9a4d858-bcf3-36b9-e3a9-449953e34569@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Dietmar Eggemann 2017-01-11 11:29:47 +00:00 committed by Ingo Molnar
parent 89ee048f3c
commit b8fd842369
1 changed files with 12 additions and 0 deletions
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12
kernel/sched/fair.c
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@ -2657,6 +2657,18 @@ static long calc_cfs_shares(struct cfs_rq *cfs_rq, struct task_group *tg)
if (tg_weight) if (tg_weight)
shares /= tg_weight; shares /= tg_weight;
/*
* MIN_SHARES has to be unscaled here to support per-CPU partitioning
* of a group with small tg->shares value. It is a floor value which is
* assigned as a minimum load.weight to the sched_entity representing
* the group on a CPU.
*
* E.g. on 64-bit for a group with tg->shares of scale_load(15)=15*1024
* on an 8-core system with 8 tasks each runnable on one CPU shares has
* to be 15*1024*1/8=1920 instead of scale_load(MIN_SHARES)=2*1024. In
* case no task is runnable on a CPU MIN_SHARES=2 should be returned
* instead of 0.
*/
if (shares < MIN_SHARES) if (shares < MIN_SHARES)
shares = MIN_SHARES; shares = MIN_SHARES;
if (shares > tg->shares) if (shares > tg->shares)