From: Shaohua Li <shli@kernel.org>
To: Joseph Qi <jiangqi903@gmail.com>
Cc: linux-block <linux-block@vger.kernel.org>,
Jens Axboe <axboe@kernel.dk>, Shaohua Li <shli@fb.com>,
boyu.mt@taobao.com, wenqing.lz@taobao.com,
qijiang.qj@alibaba-inc.com
Subject: Re: [PATCH] blk-throttle: fix possible io stall when doing upgrade
Date: Mon, 25 Sep 2017 19:48:21 -0700 [thread overview]
Message-ID: <20170926024820.2kxmluua6abvno4j@kernel.org> (raw)
In-Reply-To: <5216fe6f-deb2-8db3-a241-46f95c999a7e@gmail.com>
On Tue, Sep 26, 2017 at 09:06:57AM +0800, Joseph Qi wrote:
> Hi Shaohua,
>
> On 17/9/26 01:22, Shaohua Li wrote:
> > On Mon, Sep 25, 2017 at 06:46:42PM +0800, Joseph Qi wrote:
> >> From: Joseph Qi <qijiang.qj@alibaba-inc.com>
> >>
> >> Currently it will try to dispatch bio in throtl_upgrade_state. This may
> >> lead to io stall in the following case.
> >> Say the hierarchy is like:
> >> /-test1
> >> |-subtest1
> >> and subtest1 has 32 queued bios now.
> >>
> >> throtl_pending_timer_fn throtl_upgrade_state
> >> ------------------------------------------------------------------------
> >> upgrade to max
> >> throtl_select_dispatch
> >> throtl_schedule_next_dispatch
> >> throtl_select_dispatch
> >> throtl_schedule_next_dispatch
> >>
> >> Since throtl_select_dispatch will move queued bios from subtest1 to
> >> test1 in throtl_upgrade_state, it will then just do nothing in
> >> throtl_pending_timer_fn. As a result, queued bios won't be dispatched
> >> any more if no proper timer scheduled.
> >
> > Sorry, didn't get it. If throtl_pending_timer_fn does nothing (because
> > throtl_upgrade_state already moves bios to parent), there is no pending
> > blkcg/bio, not rearming the timer wouldn't lose anything. Am I missing
> > anything? could you please describe the failure in details?
> >
> > Thanks,
> > Shaohua
> >In normal case, throtl_pending_timer_fn tries to move bios from
> subtest1 to test1, and finally do the real issueing work when reach
> the top-level.
> But int the case above, throtl_select_dispatch in
> throtl_pending_timer_fn returns 0, because the work is done by
> throtl_upgrade_state. Then throtl_pending_timer_fn *thinks* there is
> nothing to do, but the queued bios are still in service queue of
> test1.
Still didn't get, sorry. If there are pending bios in test1, why
throtl_schedule_next_dispatch in throtl_pending_timer_fn doesn't setup the
timer?
next prev parent reply other threads:[~2017-09-26 2:48 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-09-25 10:46 [PATCH] blk-throttle: fix possible io stall when doing upgrade Joseph Qi
2017-09-25 17:22 ` Shaohua Li
2017-09-26 1:06 ` Joseph Qi
2017-09-26 2:48 ` Shaohua Li [this message]
2017-09-26 3:16 ` Joseph Qi
2017-09-27 21:38 ` Shaohua Li
2017-09-28 3:48 ` Joseph Qi
2017-09-28 11:19 ` Joseph Qi
2017-09-28 21:18 ` Shaohua Li
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