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    SubjectRe: [PATCH RFC] blk-mq: Don't IPI requests on PREEMPT_RT
    On 2020-10-23 12:21:30 [+0100], Christoph Hellwig wrote:
    > > - if (!IS_ENABLED(CONFIG_SMP) ||
    > > + if (!IS_ENABLED(CONFIG_SMP) || IS_ENABLED(CONFIG_PREEMPT_RT) ||
    > > !test_bit(QUEUE_FLAG_SAME_COMP, &rq->q->queue_flags))
    >
    > This needs a big fat comment explaining your rationale. And probably
    > a separate if statement to make it obvious as well.

    Okay.
    How much difference does it make between completing in-softirq vs
    in-IPI? I'm asking because acquiring a spinlock_t in an IPI shouldn't be
    done (as per Documentation/locking/locktypes.rst). We don't have
    anything in lockdep that will complain here on !RT and we the above we
    avoid the case on RT.

    Sebastian

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