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Date: Wed, 1 Feb 2023 17:23:48 -0800
From: Nathan Huckleberry <nhuck@...gle.com>
To: unlisted-recipients:; (no To-header on input)
Cc: Nathan Huckleberry <nhuck@...gle.com>,
Sami Tolvanen <samitolvanen@...gle.com>,
Eric Biggers <ebiggers@...nel.org>,
Alasdair Kergon <agk@...hat.com>,
Mike Snitzer <snitzer@...nel.org>, dm-devel@...hat.com,
linux-kernel@...r.kernel.org
Subject: [PATCH] dm-verity: Remove WQ_UNBOUND.
Setting WQ_UNBOUND increases scheduler latency on ARM64. This is likely
due to the asymmetric architecture of ARM64 processors.
I've been unable to reproduce the results that claim WQ_UNBOUND gives a
performance boost on x86-64.
This flag is causing performance issues for multiple subsystems within
Android. Notably, the same slowdown exists for decompression with
EROFS.
| open-prebuilt-camera | WQ_UNBOUND | ~WQ_UNBOUND |
|-----------------------|------------|---------------|
| verity wait time (us) | 11746 | 119 (-98%) |
| erofs wait time (us) | 357805 | 174205 (-51%) |
| sha256 ramdisk random read | WQ_UNBOUND | ~WQ_UNBOUND |
|----------------------------|-----------=---|-------------|
| arm64 (accelerated) | bw=42.4MiB/s | bw=212MiB/s |
| arm64 (generic) | bw=16.5MiB/s | bw=48MiB/s |
| x86_64 (generic) | bw=233MiB/s | bw=230MiB/s |
Cc: Sami Tolvanen <samitolvanen@...gle.com>
Cc: Eric Biggers <ebiggers@...nel.org>
Signed-off-by: Nathan Huckleberry <nhuck@...gle.com>
---
drivers/md/dm-verity-target.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/md/dm-verity-target.c b/drivers/md/dm-verity-target.c
index ccf5b852fbf7..020fd2341025 100644
--- a/drivers/md/dm-verity-target.c
+++ b/drivers/md/dm-verity-target.c
@@ -1399,8 +1399,8 @@ static int verity_ctr(struct dm_target *ti, unsigned argc, char **argv)
goto bad;
}
- /* WQ_UNBOUND greatly improves performance when running on ramdisk */
- wq_flags = WQ_MEM_RECLAIM | WQ_UNBOUND;
+ wq_flags = WQ_MEM_RECLAIM;
+
/*
* Using WQ_HIGHPRI improves throughput and completion latency by
* reducing wait times when reading from a dm-verity device.
--
2.39.1.456.gfc5497dd1b-goog
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