Commit-ID: b8fd8423697b9ec729c5bb91737faad84ae19985 Gitweb: http://git.kernel.org/tip/b8fd8423697b9ec729c5bb91737faad84ae19985 Author: Dietmar Eggemann <[email protected]> AuthorDate: Wed, 11 Jan 2017 11:29:47 +0000 Committer: Ingo Molnar <[email protected]> CommitDate: Sat, 14 Jan 2017 11:30:02 +0100
sched/fair: Explain why MIN_SHARES isn't scaled in calc_cfs_shares() Signed-off-by: Dietmar Eggemann <[email protected]> Signed-off-by: Peter Zijlstra (Intel) <[email protected]> Cc: Linus Torvalds <[email protected]> Cc: Mike Galbraith <[email protected]> Cc: Paul Turner <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Samuel Thibault <[email protected]> Cc: Thomas Gleixner <[email protected]> Link: http://lkml.kernel.org/r/[email protected] Signed-off-by: Ingo Molnar <[email protected]> --- kernel/sched/fair.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 2b866a2..274c747 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -2657,6 +2657,18 @@ static long calc_cfs_shares(struct cfs_rq *cfs_rq, struct task_group *tg) if (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) shares = MIN_SHARES; if (shares > tg->shares)
