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| author | Matt Fleming <matt@codeblueprint.co.uk> | 2019-08-08 22:53:01 +0300 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2019-09-03 10:17:37 +0300 |
| commit | a55c7454a8c887b226a01d7eed088ccb5374d81e (patch) | |
| tree | 43123b848008c49e81f6511613a1599c92b48fe5 /mm/khugepaged.c | |
| parent | a2cbfd46559e809c8165773b7fe8afa058b35414 (diff) | |
| download | linux-a55c7454a8c887b226a01d7eed088ccb5374d81e.tar.xz | |
sched/topology: Improve load balancing on AMD EPYC systems
SD_BALANCE_{FORK,EXEC} and SD_WAKE_AFFINE are stripped in sd_init()
for any sched domains with a NUMA distance greater than 2 hops
(RECLAIM_DISTANCE). The idea being that it's expensive to balance
across domains that far apart.
However, as is rather unfortunately explained in:
commit 32e45ff43eaf ("mm: increase RECLAIM_DISTANCE to 30")
the value for RECLAIM_DISTANCE is based on node distance tables from
2011-era hardware.
Current AMD EPYC machines have the following NUMA node distances:
node distances:
node 0 1 2 3 4 5 6 7
0: 10 16 16 16 32 32 32 32
1: 16 10 16 16 32 32 32 32
2: 16 16 10 16 32 32 32 32
3: 16 16 16 10 32 32 32 32
4: 32 32 32 32 10 16 16 16
5: 32 32 32 32 16 10 16 16
6: 32 32 32 32 16 16 10 16
7: 32 32 32 32 16 16 16 10
where 2 hops is 32.
The result is that the scheduler fails to load balance properly across
NUMA nodes on different sockets -- 2 hops apart.
For example, pinning 16 busy threads to NUMA nodes 0 (CPUs 0-7) and 4
(CPUs 32-39) like so,
$ numactl -C 0-7,32-39 ./spinner 16
causes all threads to fork and remain on node 0 until the active
balancer kicks in after a few seconds and forcibly moves some threads
to node 4.
Override node_reclaim_distance for AMD Zen.
Signed-off-by: Matt Fleming <matt@codeblueprint.co.uk>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@surriel.com>
Cc: Suravee.Suthikulpanit@amd.com
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Thomas.Lendacky@amd.com
Cc: Tony Luck <tony.luck@intel.com>
Link: https://lkml.kernel.org/r/20190808195301.13222-3-matt@codeblueprint.co.uk
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'mm/khugepaged.c')
| -rw-r--r-- | mm/khugepaged.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/mm/khugepaged.c b/mm/khugepaged.c index eaaa21b23215..ccede2425c3f 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -710,7 +710,7 @@ static bool khugepaged_scan_abort(int nid) for (i = 0; i < MAX_NUMNODES; i++) { if (!khugepaged_node_load[i]) continue; - if (node_distance(nid, i) > RECLAIM_DISTANCE) + if (node_distance(nid, i) > node_reclaim_distance) return true; } return false; |