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dm verity: stop using WQ_UNBOUND for verify_wq

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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 |

Using a alloc_workqueue() @max_active arg of num_online_cpus() only
made sense with WQ_UNBOUND. Switch the @max_active arg to 0 (aka
default, which is 256 per-cpu).

Also, eliminate 'wq_flags' since it really doesn't serve a purpose.

Cc: Sami Tolvanen <samitolvanen@google.com>
Cc: Eric Biggers <ebiggers@kernel.org>
Signed-off-by: Nathan Huckleberry <nhuck@google.com>
Reviewed-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>
This commit is contained in:
Nathan Huckleberry 2023-02-01 17:23:48 -08:00 committed by Mike Snitzer
parent 5cd6d1d53a
commit c25da5b7ba
1 changed files with 1 additions and 5 deletions
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6
drivers/md/dm-verity-target.c
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@ -1162,7 +1162,6 @@ static int verity_ctr(struct dm_target *ti, unsigned argc, char **argv)
struct dm_verity_sig_opts verify_args = {0};
struct dm_arg_set as;
unsigned int num;
unsigned int wq_flags;
unsigned long long num_ll;
int r;
int i;
@ -1399,8 +1398,6 @@ 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;
/*
* Using WQ_HIGHPRI improves throughput and completion latency by
* reducing wait times when reading from a dm-verity device.
@ -1410,8 +1407,7 @@ static int verity_ctr(struct dm_target *ti, unsigned argc, char **argv)
* will fall-back to using it for error handling (or if the bufio cache
* doesn't have required hashes).
*/
wq_flags |= WQ_HIGHPRI;
v->verify_wq = alloc_workqueue("kverityd", wq_flags, num_online_cpus());
v->verify_wq = alloc_workqueue("kverityd", WQ_MEM_RECLAIM | WQ_HIGHPRI, 0);
if (!v->verify_wq) {
ti->error = "Cannot allocate workqueue";
r = -ENOMEM;