From: Ming Lei <ming.lei@redhat.com>
To: JeffleXu <jefflexu@linux.alibaba.com>
Cc: Christoph Hellwig <hch@infradead.org>,
Jens Axboe <axboe@kernel.dk>,
linux-block@vger.kernel.org, Mike Snitzer <snitzer@redhat.com>,
dm-devel@redhat.com, Hannes Reinecke <hare@suse.de>
Subject: Re: [PATCH V5 11/12] block: add poll_capable method to support bio-based IO polling
Date: Wed, 14 Apr 2021 19:24:46 +0800 [thread overview]
Message-ID: <YHbQ/rZUPoTFUMDs@T590> (raw)
In-Reply-To: <a6d46979-810e-bc53-bc19-8acd449e3718@linux.alibaba.com>
On Wed, Apr 14, 2021 at 04:38:25PM +0800, JeffleXu wrote:
>
>
> On 4/12/21 5:38 PM, Christoph Hellwig wrote:
> > On Thu, Apr 01, 2021 at 10:19:26AM +0800, Ming Lei wrote:
> >> From: Jeffle Xu <jefflexu@linux.alibaba.com>
> >>
> >> This method can be used to check if bio-based device supports IO polling
> >> or not. For mq devices, checking for hw queue in polling mode is
> >> adequate, while the sanity check shall be implementation specific for
> >> bio-based devices. For example, dm device needs to check if all
> >> underlying devices are capable of IO polling.
> >>
> >> Though bio-based device may have done the sanity check during the
> >> device initialization phase, cacheing the result of this sanity check
> >> (such as by cacheing in the queue_flags) may not work. Because for dm
> >> devices, users could change the state of the underlying devices through
> >> '/sys/block/<dev>/io_poll', bypassing the dm device above. In this case,
> >> the cached result of the very beginning sanity check could be
> >> out-of-date. Thus the sanity check needs to be done every time 'io_poll'
> >> is to be modified.
> >
> > I really don't think thi should be a method, and I really do dislike
> > how we have all this "if (is_mq)" junk. Why can't we have a flag on
> > the gendisk that signals if the device can support polling that
> > is autoamtically set for blk-mq and as-needed by bio based drivers?
>
> That would consume one more bit of queue->queue_flags.
>
> Besides, DM/MD is somehow special here that when one of the underlying
> devices is disabled polling through '/sys/block/<dev>/io_poll',
> currently there's no mechanism notifying the above MD/DM to clear the
> previously set queue_flags. Thus the outdated queue_flags still
> indicates this DM/MD is capable of polling, while in fact one of the
> underlying device has been disabled for polling.
Right, just like there isn't queue limit progagation.
Another blocker could be that bio based queue doesn't support queue
freezing.
>
> Mike had ever suggested that we can trust the queue_flag, and clear the
> outdated queue_flags when later the IO submission or polling routine
> finally finds that the device is not capable of polling. Currently
> submit_bio_checks() will silently clear the REQ_HIPRI flag and still
> submit the bio when the device is actually not capable of polling. To
> fix the issue, could we break the submission and return an error code in
> submit_bio_checks() if the device is not capable of polling when
> submitting HIPRI bio?
I think we may just leave it alone, if underlying queue becomes not pollable,
the bio still can be submitted & completed via IRQ, just not efficient enough.
Thanks,
Ming
next prev parent reply other threads:[~2021-04-14 11:25 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-01 2:19 [PATCH V5 00/12] block: support bio based io polling Ming Lei
2021-04-01 2:19 ` [PATCH V5 01/12] block: add helper of blk_queue_poll Ming Lei
2021-04-01 2:19 ` [PATCH V5 02/12] block: add one helper to free io_context Ming Lei
2021-04-01 2:19 ` [PATCH V5 03/12] block: create io poll context for submission and poll task Ming Lei
2021-04-12 10:19 ` Christoph Hellwig
2021-04-01 2:19 ` [PATCH V5 04/12] block: add req flag of REQ_POLL_CTX Ming Lei
2021-04-01 2:19 ` [PATCH V5 05/12] block: add new field into 'struct bvec_iter' Ming Lei
2021-04-12 9:26 ` Christoph Hellwig
2021-04-13 9:36 ` Ming Lei
2021-04-01 2:19 ` [PATCH V5 06/12] block/mq: extract one helper function polling hw queue Ming Lei
2021-04-12 9:29 ` Christoph Hellwig
2021-04-01 2:19 ` [PATCH V5 07/12] block: prepare for supporting bio_list via other link Ming Lei
2021-04-12 10:18 ` Christoph Hellwig
2021-04-12 11:37 ` Ming Lei
2021-04-01 2:19 ` [PATCH V5 08/12] block: use per-task poll context to implement bio based io polling Ming Lei
2021-04-12 9:54 ` Christoph Hellwig
2021-04-12 10:20 ` Ming Lei
2021-04-12 10:29 ` Christoph Hellwig
2021-04-12 11:42 ` Ming Lei
2021-04-12 10:16 ` Christoph Hellwig
2021-04-12 10:37 ` Ming Lei
2021-04-01 2:19 ` [PATCH V5 09/12] blk-mq: limit hw queues to be polled in each blk_poll() Ming Lei
2021-04-01 2:19 ` [PATCH V5 10/12] block: add queue_to_disk() to get gendisk from request_queue Ming Lei
2021-04-12 12:52 ` Jens Axboe
2021-04-01 2:19 ` [PATCH V5 11/12] block: add poll_capable method to support bio-based IO polling Ming Lei
2021-04-12 9:38 ` Christoph Hellwig
2021-04-14 8:38 ` JeffleXu
2021-04-14 11:24 ` Ming Lei [this message]
2021-04-15 1:34 ` JeffleXu
2021-04-15 7:43 ` Ming Lei
2021-04-15 9:21 ` JeffleXu
2021-04-15 10:06 ` Ming Lei
2021-04-15 11:21 ` JeffleXu
2021-04-15 13:08 ` Ming Lei
2021-04-16 8:00 ` [PATCH] block: introduce QUEUE_FLAG_POLL_CAP flag Jeffle Xu
2021-04-16 8:42 ` JeffleXu
2021-04-16 9:07 ` Ming Lei
2021-04-16 10:20 ` JeffleXu
2021-04-17 14:06 ` JeffleXu
2021-04-19 2:21 ` Ming Lei
2021-04-19 5:40 ` JeffleXu
2021-04-19 13:36 ` Ming Lei
2021-04-20 7:25 ` JeffleXu
2021-04-01 2:19 ` [PATCH V5 12/12] dm: support IO polling for bio-based dm device Ming Lei
2021-04-09 15:39 ` [PATCH V5 00/12] block: support bio based io polling Ming Lei
2021-04-12 9:46 ` Christoph Hellwig
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