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

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

[Dietmar Eggemann]

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@arm.com>
---

Besides the issue with load_above_capacity when it comes to different
fixed point units for load "[PATCH] sched/fair: Fix load_above_capacity
fixed point arithmetic width" there are similar issues for shares in
calc_cfs_shares() as well as wl in effective_load().

 kernel/sched/fair.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 61d485421bed..18f80c4c7737 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2530,8 +2530,8 @@ static long calc_cfs_shares(struct cfs_rq *cfs_rq, struct task_group *tg)
 	if (tg_weight)
 		shares /= tg_weight;
 
-	if (shares < MIN_SHARES)
-		shares = MIN_SHARES;
+	if (shares < scale_load(MIN_SHARES))
+		shares = scale_load(MIN_SHARES);
 	if (shares > tg->shares)
 		shares = tg->shares;
 
@@ -5023,9 +5023,9 @@ 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
-- 
1.9.1

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

[tip-bot for Dietmar Eggemann]

Commit-ID:  ab522e33f91799661aad47bebb691f241a9f6bb8
Gitweb:     http://git.kernel.org/tip/ab522e33f91799661aad47bebb691f241a9f6bb8
Author:     Dietmar Eggemann <dietmar.eggemann@arm.com>
AuthorDate: Mon, 22 Aug 2016 15:00:41 +0100
Committer:  Ingo Molnar <mingo@kernel.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@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: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1471874441-24701-1-git-send-email-dietmar.eggemann@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.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