From: Jens Axboe <axboe@kernel.dk>
To: Christoph Hellwig <hch@infradead.org>
Cc: linux-block@vger.kernel.org
Subject: Re: [PATCH 01/11] nvme: provide optimized poll function for separate poll queues
Date: Fri, 16 Nov 2018 08:22:15 -0700 [thread overview]
Message-ID: <9f994097-7966-c629-892e-3f43344541ac@kernel.dk> (raw)
In-Reply-To: <20181116083539.GC9023@infradead.org>
On 11/16/18 1:35 AM, Christoph Hellwig wrote:
> On Thu, Nov 15, 2018 at 12:51:25PM -0700, Jens Axboe wrote:
>> If we have separate poll queues, we know that they aren't using
>> interrupts. Hence we don't need to disable interrupts around
>> finding completions.
>>
>> Provide a separate set of blk_mq_ops for such devices.
>
> This looks ok, but I'd prefer if we could offer to just support
> polling with the separate queue. That way we get ourselves out of
> all kinds of potential races of the interrupt path vs poll path.
As Keith mentioned, we do use polling to find missing completions
in case of timeouts. And that has actually been really useful.
I'd rather keep such a change separate. If we do go down that
route, then there are more optimizations we can make.
Finally, let's not forget that polling is/was still a win even
if we did trigger interrupts. That's how NVMe has been since
polling was introduced. While the newer stuff is a lot more
efficient, I don't think we should totally abandon an easy opt-in
for polling for hardware unless we have strong reasons to do so.
--
Jens Axboe
next prev parent reply other threads:[~2018-11-16 15:22 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-15 19:51 [PATCHSET v2 0/11] Various block optimizations Jens Axboe
2018-11-15 19:51 ` [PATCH 01/11] nvme: provide optimized poll function for separate poll queues Jens Axboe
2018-11-16 8:35 ` Christoph Hellwig
2018-11-16 15:22 ` Jens Axboe [this message]
2018-11-15 19:51 ` [PATCH 02/11] block: add queue_is_mq() helper Jens Axboe
2018-11-16 8:35 ` Christoph Hellwig
2018-11-15 19:51 ` [PATCH 03/11] blk-rq-qos: inline check for q->rq_qos functions Jens Axboe
2018-11-16 8:38 ` Christoph Hellwig
2018-11-16 15:18 ` Jens Axboe
2018-11-15 19:51 ` [PATCH 04/11] block: avoid ordered task state change for polled IO Jens Axboe
2018-11-16 8:41 ` Christoph Hellwig
2018-11-16 15:32 ` Jens Axboe
2018-11-15 19:51 ` [PATCH 05/11] block: add polled wakeup task helper Jens Axboe
2018-11-16 8:41 ` Christoph Hellwig
2018-11-15 19:51 ` [PATCH 06/11] block: have ->poll_fn() return number of entries polled Jens Axboe
2018-11-15 19:51 ` [PATCH 07/11] blk-mq: when polling for IO, look for any completion Jens Axboe
2018-11-16 8:43 ` Christoph Hellwig
2018-11-16 15:19 ` Jens Axboe
2018-11-16 16:57 ` Jens Axboe
2018-11-15 19:51 ` [PATCH 08/11] block: make blk_poll() take a parameter on whether to spin or not Jens Axboe
2018-11-15 19:51 ` [PATCH 09/11] blk-mq: ensure mq_ops ->poll() is entered at least once Jens Axboe
2018-11-15 19:51 ` [PATCH 10/11] block: for async O_DIRECT, mark us as polling if asked to Jens Axboe
2018-11-16 8:47 ` Christoph Hellwig
2018-11-16 8:48 ` Christoph Hellwig
2018-11-16 15:19 ` Jens Axboe
2018-11-15 19:51 ` [PATCH 11/11] block: don't plug for aio/O_DIRECT HIPRI IO Jens Axboe
2018-11-16 8:49 ` Christoph Hellwig
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