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>
Bug: 233247259
Change-Id: Iea437fcfaa978a1389a57ef4d4adcb976d89089c
(cherry picked from commit c25da5b7baf1d243e6612ba2b97e2a2c4a1376f6)
Signed-off-by: Nathan Huckleberry <nhuck@google.com>
2c07e6e724