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[ Upstream commit a46c27026da10a126dd870f7b65380010bd20db5 ] Kernel parameter of `isolcpus=` or 'nohz_full=' are used to isolate CPUs for specific task, and it isn't expected to let block IO disturb these CPUs. blk-mq kworker shouldn't be scheduled on isolated CPUs. Also if isolated CPUs is run for blk-mq kworker, long block IO latency can be caused. Kernel workqueue only respects CPU isolation for WQ_UNBOUND, for bound WQ, the responsibility is on user because CPU is specified as WQ API parameter, such as mod_delayed_work_on(cpu), queue_delayed_work_on(cpu) and queue_work_on(cpu). So not run blk-mq kworker on isolated CPUs by removing isolated CPUs from hctx->cpumask. Meantime use queue map to check if all CPUs in this hw queue are offline instead of hctx->cpumask, this way can avoid any cost in fast IO code path, and is safe since hctx->cpumask are only used in the two cases. Cc: Tim Chen <tim.c.chen@linux.intel.com> Cc: Juri Lelli <juri.lelli@redhat.com> Cc: Andrew Theurer <atheurer@redhat.com> Cc: Joe Mario <jmario@redhat.com> Cc: Sebastian Jug <sejug@redhat.com> Cc: Frederic Weisbecker <frederic@kernel.org> Cc: Bart Van Assche <bvanassche@acm.org> Cc: Tejun Heo <tj@kernel.org> Tesed-by: Joe Mario <jmario@redhat.com> Signed-off-by: Ming Lei <ming.lei@redhat.com> Reviewed-by: Ewan D. Milne <emilne@redhat.com> Link: https://lore.kernel.org/r/20240322021244.1056223-1-ming.lei@redhat.com Signed-off-by: Jens Axboe <axboe@kernel.dk> Stable-dep-of: 10845a105bbc ("blk-mq: skip CPU offline notify on unmapped hctx") Signed-off-by: Sasha Levin <sashal@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.