linux-kernel - [tip:sched/core] sched/fair: Fix fixed point arithmetic width for shares and effective load

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Date:   Fri, 30 Sep 2016 04:55:57 -0700
From:   tip-bot for Dietmar Eggemann <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     tglx@...utronix.de, hpa@...or.com, peterz@...radead.org,
        efault@....de, torvalds@...ux-foundation.org, mingo@...nel.org,
        dietmar.eggemann@....com, linux-kernel@...r.kernel.org
Subject: [tip:sched/core] sched/fair: Fix fixed point arithmetic width for
 shares and effective load

Commit-ID:  ab522e33f91799661aad47bebb691f241a9f6bb8
Gitweb:     http://git.kernel.org/tip/ab522e33f91799661aad47bebb691f241a9f6bb8
Author:     Dietmar Eggemann <dietmar.eggemann@....com>
AuthorDate: Mon, 22 Aug 2016 15:00:41 +0100
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Fri, 30 Sep 2016 10:53:19 +0200

sched/fair: Fix fixed point arithmetic width for shares and effective load

Since commit:

  2159197d6677 ("sched/core: Enable increased load resolution on 64-bit kernels")

we now have two different fixed point units for load:

- 'shares' in calc_cfs_shares() has 20 bit fixed point unit on 64-bit
  kernels. Therefore use scale_load() on MIN_SHARES.

- 'wl' in effective_load() has 10 bit fixed point unit. Therefore use
  scale_load_down() on tg->shares which has 20 bit fixed point unit on
  64-bit kernels.

Signed-off-by: Dietmar Eggemann <dietmar.eggemann@....com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Mike Galbraith <efault@....de>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Link: http://lkml.kernel.org/r/1471874441-24701-1-git-send-email-dietmar.eggemann@arm.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 kernel/sched/fair.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 8fb4d19..786ef94 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5017,9 +5017,9 @@ static long effective_load(struct task_group *tg, int cpu, long wl, long wg)
 		 * wl = S * s'_i; see (2)
 		 */
 		if (W > 0 && w < W)
-			wl = (w * (long)tg->shares) / W;
+			wl = (w * (long)scale_load_down(tg->shares)) / W;
 		else
-			wl = tg->shares;
+			wl = scale_load_down(tg->shares);
 
 		/*
 		 * Per the above, wl is the new se->load.weight value; since