From: Jens Axboe <axboe@kernel.dk>
To: Xiaoguang Wang <xiaoguang.wang@linux.alibaba.com>,
linux-block@vger.kernel.org
Cc: hch@infradead.org, joseph.qi@linux.alibaba.com
Subject: Re: [RFC] blk-mq: don't plug for HIPRI IO
Date: Wed, 28 Oct 2020 08:42:39 -0600 [thread overview]
Message-ID: <80adbefe-2660-34a4-1242-c3db9cd689a6@kernel.dk> (raw)
In-Reply-To: <20201027132951.121812-1-xiaoguang.wang@linux.alibaba.com>
On 10/27/20 7:29 AM, Xiaoguang Wang wrote:
> Commit cb700eb3faa4 ("block: don't plug for aio/O_DIRECT HIPRI IO")
> only does not call blk_start_plug() or blk_finish_plug for HIPRI IO
> in __blkdev_direct_IO(), but if upper layer subsystem, such as io_uring,
> still initializes valid plug, block layer may still plug HIPRI IO.
> To disable plug for HIPRI IO completely, do it in blk_mq_plug().
There's something funky going on with plugging and polled IO. I tried
to improve the io_uring plugging, so we don't plug for polled IO (or for
non-bdev IO in general), and it tanked performance here from ~2.5M IOPS
to ~1.4M IOPS. Thinking I had made some sort of mistake, I just tried
your patch alone, and I see the same performance drop.
This doesn't make a lot of sense, so some investigation is needed.
--
Jens Axboe
prev parent reply other threads:[~2020-10-28 22:04 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-27 13:29 [RFC] blk-mq: don't plug for HIPRI IO Xiaoguang Wang
2020-10-27 19:33 ` Christoph Hellwig
2020-10-28 14:42 ` Jens Axboe [this message]
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