The following commit has been merged into the sched/core branch of tip:
Commit-ID: c8987ae5af793a73e2c0d6ce804d8ff454ea377c
Gitweb:
https://git.kernel.org/tip/c8987ae5af793a73e2c0d6ce804d8ff454ea377c
Author: Barry Song <song.bao....@hisilicon.com>
AuthorDate: Sun, 21 Mar 2021 11:14:32 +13:00
Committer: Peter Zijlstra <pet...@infradead.org>
CommitterDate: Tue, 23 Mar 2021 16:01:59 +01:00
sched/fair: Optimize test_idle_cores() for !SMT
update_idle_core() is only done for the case of sched_smt_present.
but test_idle_cores() is done for all machines even those without
SMT.
This can contribute to up 8%+ hackbench performance loss on a
machine like kunpeng 920 which has no SMT. This patch removes the
redundant test_idle_cores() for !SMT machines.
Hackbench is ran with -g {2..14}, for each g it is ran 10 times to get
an average.
$ numactl -N 0 hackbench -p -T -l 20000 -g $1
The below is the result of hackbench w/ and w/o this patch:
g= 2 4 6 8 10 12 14
w/o: 1.8151 3.8499 5.5142 7.2491 9.0340 10.7345 12.0929
w/ : 1.8428 3.7436 5.4501 6.9522 8.2882 9.9535 11.3367
+4.1% +8.3% +7.3% +6.3%
Signed-off-by: Barry Song <song.bao....@hisilicon.com>
Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
Reviewed-by: Vincent Guittot <vincent.guit...@linaro.org>
Acked-by: Mel Gorman <mgor...@suse.de>
Link: https://lkml.kernel.org/r/20210320221432.924-1-song.bao....@hisilicon.com
---
kernel/sched/fair.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 6aad028..aaa0dfa 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6038,9 +6038,11 @@ static inline bool test_idle_cores(int cpu, bool def)
{
struct sched_domain_shared *sds;
- sds = rcu_dereference(per_cpu(sd_llc_shared, cpu));
- if (sds)
- return READ_ONCE(sds->has_idle_cores);
+ if (static_branch_likely(&sched_smt_present)) {
+ sds = rcu_dereference(per_cpu(sd_llc_shared, cpu));
+ if (sds)
+ return READ_ONCE(sds->has_idle_cores);
+ }
return def;
}
