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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>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.