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From: Oleg Nesterov <oleg@redhat.com>
To: Jens Axboe <axboe@fb.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Jens Axboe <axboe@kernel.dk>, Josef Bacik <josef@toxicpanda.com>,
	Kernel Team <Kernel-team@fb.com>,
	"linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
	Ingo Molnar <mingo@kernel.org>
Subject: Re: [PATCH 1/2] wait: add wq_has_multiple_sleepers helper
Date: Thu, 11 Jul 2019 13:45:43 +0200	[thread overview]
Message-ID: <20190711114543.GA14901@redhat.com> (raw)
In-Reply-To: <752dbdc9-945d-e70c-e6f3-0c48932c7f60@fb.com>

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.


  reply	other threads:[~2019-07-11 11:45 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-07-10 19:52 [PATCH 1/2] wait: add wq_has_multiple_sleepers helper Josef Bacik
2019-07-10 19:52 ` [PATCH 2/2] rq-qos: fix missed wake-ups in rq_qos_throttle Josef Bacik
2019-07-10 20:23 ` [PATCH 1/2] wait: add wq_has_multiple_sleepers helper Jens Axboe
2019-07-10 20:35   ` Peter Zijlstra
2019-07-10 20:39     ` Jens Axboe
2019-07-11 11:45       ` Oleg Nesterov [this message]
2019-07-11 13:40         ` Oleg Nesterov
2019-07-11 19:21           ` Josef Bacik
2019-07-12  8:05             ` Oleg Nesterov

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