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Date:   Thu, 11 Jul 2019 13:45:43 +0200
From:   Oleg Nesterov <oleg@redhat.com>
To:     Jens Axboe <axboe@fb.com>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Jens Axboe <axboe@kernel.dk>,
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        Kernel Team <Kernel-team@fb.com>,
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        Ingo Molnar <mingo@kernel.org>
Subject: Re: [PATCH 1/2] wait: add wq_has_multiple_sleepers helper
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Jens,

I managed to convince myself I understand why 2/2 needs this change...
But rq_qos_wait() still looks suspicious to me. Why can't the main loop
"break" right after io_schedule()? rq_qos_wake_function() either sets
data->got_token = true or it doesn't wakeup the waiter sleeping in
io_schedule()

This means that data.got_token = F at the 2nd iteration is only possible
after a spurious wakeup, right? But in this case we need to set state =
TASK_UNINTERRUPTIBLE again to avoid busy-wait looping ?

Oleg.