Commit-ID: 2159197d66770ec01f75c93fb11dc66df81fd45b
Gitweb: http://git.kernel.org/tip/2159197d66770ec01f75c93fb11dc66df81fd45b
Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate: Thu, 28 Apr 2016 12:49:38 +0200
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Thu, 5 May 2016 09:24:00 +0200
sched/core: Enable increased load resolution on 64-bit kernels
Mike ran into the low load resolution limitation on his big machine.
So reenable these bits; nobody could ever reproduce/analyze the
reported power usage claim and Google has been running with this for
years as well.
Reported-by: Mike Galbraith <umgwanakikbuti@xxxxxxxxx>
Tested-by: Mike Galbraith <umgwanakikbuti@xxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Mike Galbraith <efault@xxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: linux-kernel@xxxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
kernel/sched/sched.h | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 0b6a838..066a4c2 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -49,11 +49,13 @@ static inline void cpu_load_update_active(struct rq *this_rq) { }
* and does not change the user-interface for setting shares/weights.
*
* We increase resolution only if we have enough bits to allow this increased
- * resolution (i.e. BITS_PER_LONG > 32). The costs for increasing resolution
- * when BITS_PER_LONG <= 32 are pretty high and the returns do not justify the
- * increased costs.
+ * resolution (i.e. 64bit). The costs for increasing resolution when 32bit are
+ * pretty high and the returns do not justify the increased costs.
+ *
+ * Really only required when CONFIG_FAIR_GROUP_SCHED is also set, but to
+ * increase coverage and consistency always enable it on 64bit platforms.
*/
-#if 0 /* BITS_PER_LONG > 32 -- currently broken: it increases power usage under light load */
+#ifdef CONFIG_64BIT
# define SCHED_LOAD_RESOLUTION 10
# define scale_load(w) ((w) << SCHED_LOAD_RESOLUTION)
# define scale_load_down(w) ((w) >> SCHED_LOAD_RESOLUTION)
--
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