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    SubjectRe: [PATCH 2/2] blk-mq: simplify queue mapping & schedule with each possisble CPU
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    Hi ming 

    Thanks for your kindly response.

    On 01/17/2018 02:22 PM, Ming Lei wrote:
    > This warning can't be removed completely, for example, the CPU figured
    > in blk_mq_hctx_next_cpu(hctx) can be put on again just after the
    > following call returns and before __blk_mq_run_hw_queue() is scheduled
    > to run.
    >
    > kblockd_mod_delayed_work_on(blk_mq_hctx_next_cpu(hctx), &hctx->run_work, msecs_to_jiffies(msecs))
    We could use cpu_active in __blk_mq_run_hw_queue() to narrow the window.
    There is a big gap between cpu_online and cpu_active. rebind_workers is also between them.

    >
    > Just be curious how you trigger this issue? And is it triggered in CPU
    > hotplug stress test? Or in a normal use case?

    In fact, this is my own investigation about whether the .queue_rq to one hardware queue could be executed on
    the cpu where it is not mapped. Finally, found this hole when cpu hotplug.
    I did the test on NVMe device which has 1-to-1 mapping between cpu and hctx.
    - A special patch that could hold some requests on ctx->rq_list though .get_budget
    - A script issues IOs with fio
    - A script online/offline the cpus continuously
    At first, just the warning above. Then after this patch was introduced, panic came up.

    Thanks
    Jianchao

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