blk-mq: avoid housekeeping CPUs scheduling a worker on a non-housekeeping CPU

hulk inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I7ZBTV


CVE: N/A

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When NOHZ_FULL is enabled, such as in HPC situation, CPUs are divided
into housekeeping CPUs and non-housekeeping CPUs. Non-housekeeping CPUs
are NOHZ_FULL CPUs and are often monopolized by the userspace process,
such HPC application process. Any sort of interruption is not expected.

blk_mq_hctx_next_cpu() selects each cpu in 'hctx->cpumask' alternately
to schedule the work thread blk_mq_run_work_fn(). When 'hctx->cpumask'
contains housekeeping CPU and non-housekeeping CPU at the same time, a
housekeeping CPU, which want to request a IO, may schedule a worker on a
non-housekeeping CPU. This may affect the performance of the userspace
application running on non-housekeeping CPUs.

So let's just schedule the worker thread on the current CPU when the
current CPU is housekeeping CPU.

Signed-off-by: Xiongfeng Wang <wangxiongfeng2@huawei.com>