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author | Valentin Schneider <valentin.schneider@arm.com> | 2019-04-09 20:35:45 +0300 |
---|---|---|
committer | Ingo Molnar <mingo@kernel.org> | 2019-04-10 10:41:34 +0300 |
commit | 67d4f6ff2fb69e02bd6365a91ca3939b7a14deac (patch) | |
tree | 15fb07ca42187919fca59d8c2d2f36bf65790b8e /kernel/sched | |
parent | d8743230c9f4e92f370ecd2a90c680ddcede6ae5 (diff) | |
download | linux-67d4f6ff2fb69e02bd6365a91ca3939b7a14deac.tar.xz |
sched/topology: Skip duplicate group rewrites in build_sched_groups()
While staring at build_sched_domains(), I realized that get_group()
does several duplicate (thus useless) writes.
If you take the Arm Juno r0 (LITTLEs = [0, 3, 4, 5], bigs = [1, 2]), the
sched_group build flow would look like this:
('MC[cpu]->sg' means 'per_cpu_ptr(&tl->data->sg, cpu)' with 'tl == MC')
build_sched_groups(MC[CPU0]->sd, CPU0)
get_group(0) -> MC[CPU0]->sg
get_group(3) -> MC[CPU3]->sg
get_group(4) -> MC[CPU4]->sg
get_group(5) -> MC[CPU5]->sg
build_sched_groups(DIE[CPU0]->sd, CPU0)
get_group(0) -> DIE[CPU0]->sg
get_group(1) -> DIE[CPU1]->sg <=================+
|
build_sched_groups(MC[CPU1]->sd, CPU1) |
get_group(1) -> MC[CPU1]->sg |
get_group(2) -> MC[CPU2]->sg |
|
build_sched_groups(DIE[CPU1]->sd, CPU1) ^
get_group(1) -> DIE[CPU1]->sg } We've set up these two up here!
get_group(3) -> DIE[CPU0]->sg }
From this point on, we will only use sched_groups that have been
previously visited & initialized. The only new operation will
be which group pointer we affect to sd->groups.
On the Juno r0 we get 32 get_group() calls, every single one of them
writing to a sched_group->cpumask. However, all of the data structures
we need are set up after 8 visits (see above).
Return early from get_group() if we've already visited (and thus
initialized) the sched_group we're looking at. Overlapping domains
are not affected as they do not use build_sched_groups().
Tested on a Juno and a 2 * (Xeon E5-2690) system.
( FWIW I initially checked the refs for both sg && sg->sgc, but figured if
they weren't both 0 or > 1 then something must have gone wrong, so I
threw in a WARN_ON(). )
No change in functionality intended.
Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/sched')
-rw-r--r-- | kernel/sched/topology.c | 12 |
1 files changed, 9 insertions, 3 deletions
diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c index 90e1a870fb0d..c65b31e9458b 100644 --- a/kernel/sched/topology.c +++ b/kernel/sched/topology.c @@ -1059,6 +1059,7 @@ static struct sched_group *get_group(int cpu, struct sd_data *sdd) struct sched_domain *sd = *per_cpu_ptr(sdd->sd, cpu); struct sched_domain *child = sd->child; struct sched_group *sg; + bool already_visited; if (child) cpu = cpumask_first(sched_domain_span(child)); @@ -1066,9 +1067,14 @@ static struct sched_group *get_group(int cpu, struct sd_data *sdd) sg = *per_cpu_ptr(sdd->sg, cpu); sg->sgc = *per_cpu_ptr(sdd->sgc, cpu); - /* For claim_allocations: */ - atomic_inc(&sg->ref); - atomic_inc(&sg->sgc->ref); + /* Increase refcounts for claim_allocations: */ + already_visited = atomic_inc_return(&sg->ref) > 1; + /* sgc visits should follow a similar trend as sg */ + WARN_ON(already_visited != (atomic_inc_return(&sg->sgc->ref) > 1)); + + /* If we have already visited that group, it's already initialized. */ + if (already_visited) + return sg; if (child) { cpumask_copy(sched_group_span(sg), sched_domain_span(child)); |