From: Christoph Hellwig <hch@infradead.org>
To: Linus Walleij <linus.walleij@linaro.org>
Cc: Jens Axboe <axboe@kernel.dk>,
Ulf Hansson <ulf.hansson@linaro.org>,
Paolo Valente <paolo.valente@linaro.org>,
Christoph Hellwig <hch@infradead.org>,
Arnd Bergmann <arnd@arndb.de>,
Bart Van Assche <bart.vanassche@sandisk.com>,
Jan Kara <jack@suse.cz>, Tejun Heo <tj@kernel.org>,
linux-block@vger.kernel.org,
Linux-Kernal <linux-kernel@vger.kernel.org>,
Mark Brown <broonie@kernel.org>, Hannes Reinecke <hare@suse.de>,
Grant Likely <grant.likely@secretlab.ca>,
James Bottomley <James.Bottomley@hansenpartnership.com>,
Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Subject: Re: [PATCH 00/14] introduce the BFQ-v0 I/O scheduler as an extra scheduler
Date: Fri, 28 Oct 2016 08:29:08 -0700 [thread overview]
Message-ID: <20161028152908.GA21341@infradead.org> (raw)
In-Reply-To: <CACRpkda0fmPdM2WZ_gtW=T7xvMfP_4ErtNZseExN2AggzZbcDQ@mail.gmail.com>
On Fri, Oct 28, 2016 at 11:32:21AM +0200, Linus Walleij wrote:
> So I'm not just complaining by the way, I'm trying to fix this. Also
> Bartlomiej from Samsung has done some stabs at switching MMC/SD
> to blk-mq. I just rebased my latest stab at a na�ve switch to blk-mq
> to v4.9-rc2 with these results.
>
> The patch to enable MQ looks like this:
> https://git.kernel.org/cgit/linux/kernel/git/linusw/linux-stericsson.git/commit/?h=mmc-mq&id=8f79b527e2e854071d8da019451da68d4753f71d
>
> I run these tests directly after boot with cold caches. The results
> are consistent: I ran the same commands 10 times in a row.
A couple comments from a quick look over the patch:
In the changelog you complain:
". Lack of front- and back-end merging in the MQ block layer creating
several small requests instead of a few large ones."
In blk-mq merging is controller by the BLK_MQ_F_SHOULD_MERGE and
BLK_MQ_F_SG_MERGE flags. You set the former, but not the latter.
BLK_MQ_F_SG_MERGE controls wether multiple physical contiguous pages get
merged into a single segment. For a dd after a fresh boot that is
probably very common. Except for the polarity of the merge flags the
basic merge functionality between the legacy and blk-mq path should be
the same, and if they aren't you've found a bug we need to address.
You also say that you disable the pipelining. How much of a performance
gain did this feature give when added? How much does just removing that
on it's own cost you? While I think that features is rather messy and
should be avoided if possible I don't see how it's impossible to
implement in blk-mq. If you just increase your queue depth and use
the old scheme you should get it - if you currently can't handle the
second command for some reason (i.e. the special request magic) you
can just return BLK_MQ_RQ_QUEUE_BUSY from the queue_rq function.
WARNING: multiple messages have this Message-ID (diff)
From: Christoph Hellwig <hch@infradead.org>
To: Linus Walleij <linus.walleij@linaro.org>
Cc: Jens Axboe <axboe@kernel.dk>,
Ulf Hansson <ulf.hansson@linaro.org>,
Paolo Valente <paolo.valente@linaro.org>,
Christoph Hellwig <hch@infradead.org>,
Arnd Bergmann <arnd@arndb.de>,
Bart Van Assche <bart.vanassche@sandisk.com>,
Jan Kara <jack@suse.cz>, Tejun Heo <tj@kernel.org>,
linux-block@vger.kernel.org,
Linux-Kernal <linux-kernel@vger.kernel.org>,
Mark Brown <broonie@kernel.org>, Hannes Reinecke <hare@suse.de>,
Grant Likely <grant.likely@secretlab.ca>,
James Bottomley <James.Bottomley@hansenpartnership.com>,
Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Subject: Re: [PATCH 00/14] introduce the BFQ-v0 I/O scheduler as an extra scheduler
Date: Fri, 28 Oct 2016 08:29:08 -0700 [thread overview]
Message-ID: <20161028152908.GA21341@infradead.org> (raw)
In-Reply-To: <CACRpkda0fmPdM2WZ_gtW=T7xvMfP_4ErtNZseExN2AggzZbcDQ@mail.gmail.com>
On Fri, Oct 28, 2016 at 11:32:21AM +0200, Linus Walleij wrote:
> So I'm not just complaining by the way, I'm trying to fix this. Also
> Bartlomiej from Samsung has done some stabs at switching MMC/SD
> to blk-mq. I just rebased my latest stab at a naïve switch to blk-mq
> to v4.9-rc2 with these results.
>
> The patch to enable MQ looks like this:
> https://git.kernel.org/cgit/linux/kernel/git/linusw/linux-stericsson.git/commit/?h=mmc-mq&id=8f79b527e2e854071d8da019451da68d4753f71d
>
> I run these tests directly after boot with cold caches. The results
> are consistent: I ran the same commands 10 times in a row.
A couple comments from a quick look over the patch:
In the changelog you complain:
". Lack of front- and back-end merging in the MQ block layer creating
several small requests instead of a few large ones."
In blk-mq merging is controller by the BLK_MQ_F_SHOULD_MERGE and
BLK_MQ_F_SG_MERGE flags. You set the former, but not the latter.
BLK_MQ_F_SG_MERGE controls wether multiple physical contiguous pages get
merged into a single segment. For a dd after a fresh boot that is
probably very common. Except for the polarity of the merge flags the
basic merge functionality between the legacy and blk-mq path should be
the same, and if they aren't you've found a bug we need to address.
You also say that you disable the pipelining. How much of a performance
gain did this feature give when added? How much does just removing that
on it's own cost you? While I think that features is rather messy and
should be avoided if possible I don't see how it's impossible to
implement in blk-mq. If you just increase your queue depth and use
the old scheme you should get it - if you currently can't handle the
second command for some reason (i.e. the special request magic) you
can just return BLK_MQ_RQ_QUEUE_BUSY from the queue_rq function.
next prev parent reply other threads:[~2016-10-28 15:29 UTC|newest]
Thread overview: 66+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-10-26 9:27 [PATCH 00/14] introduce the BFQ-v0 I/O scheduler as an extra scheduler Paolo Valente
2016-10-26 9:27 ` [PATCH 01/14] block, bfq: " Paolo Valente
2016-10-26 9:27 ` [PATCH 02/14] block, bfq: add full hierarchical scheduling and cgroups support Paolo Valente
2016-10-26 9:27 ` [PATCH 03/14] block, bfq: improve throughput boosting Paolo Valente
2016-10-26 9:27 ` [PATCH 04/14] block, bfq: modify the peak-rate estimator Paolo Valente
2016-10-26 9:27 ` [PATCH 05/14] block, bfq: add more fairness with writes and slow processes Paolo Valente
2016-10-26 9:27 ` [PATCH 06/14] block, bfq: improve responsiveness Paolo Valente
2016-10-26 9:28 ` [PATCH 07/14] block, bfq: reduce I/O latency for soft real-time applications Paolo Valente
2016-10-26 9:28 ` [PATCH 08/14] block, bfq: preserve a low latency also with NCQ-capable drives Paolo Valente
2016-10-26 9:28 ` [PATCH 09/14] block, bfq: reduce latency during request-pool saturation Paolo Valente
2016-10-26 10:19 ` [PATCH 00/14] introduce the BFQ-v0 I/O scheduler as an extra scheduler Christoph Hellwig
2016-10-26 11:34 ` Jan Kara
2016-10-26 15:05 ` Bart Van Assche
2016-10-26 15:13 ` Arnd Bergmann
2016-10-26 15:29 ` Christoph Hellwig
2016-10-26 15:32 ` Jens Axboe
2016-10-26 16:04 ` Paolo Valente
2016-10-26 16:04 ` Paolo Valente
2016-10-26 16:12 ` Jens Axboe
2016-10-27 9:26 ` Jan Kara
2016-10-27 14:34 ` Grozdan
2016-10-27 15:55 ` Heinz Diehl
2016-10-27 16:28 ` Jens Axboe
2016-10-27 16:26 ` Jens Axboe
2016-10-28 7:59 ` Jan Kara
2016-10-28 14:10 ` Jens Axboe
2016-10-27 17:32 ` Ulf Hansson
2016-10-27 17:43 ` Jens Axboe
2016-10-27 18:13 ` Ulf Hansson
2016-10-27 18:21 ` Jens Axboe
2016-10-27 19:34 ` Ulf Hansson
2016-10-27 21:08 ` Jens Axboe
2016-10-27 22:27 ` Linus Walleij
2016-10-28 9:32 ` Linus Walleij
2016-10-28 9:32 ` Linus Walleij
2016-10-28 14:22 ` Jens Axboe
2016-10-28 20:38 ` Linus Walleij
2016-10-28 15:29 ` Christoph Hellwig [this message]
2016-10-28 15:29 ` Christoph Hellwig
2016-10-28 21:09 ` Linus Walleij
2016-10-28 21:09 ` Linus Walleij
2016-10-28 15:30 ` Jens Axboe
2016-10-28 15:58 ` Bartlomiej Zolnierkiewicz
2016-10-28 16:05 ` Arnd Bergmann
2016-10-28 17:17 ` Mark Brown
2016-10-28 14:07 ` Jens Axboe
2016-10-28 6:36 ` Ulf Hansson
2016-10-28 14:17 ` Jens Axboe
2016-10-28 17:12 ` Mark Brown
2016-10-27 19:41 ` Mark Brown
2016-10-27 19:45 ` Christoph Hellwig
2016-10-27 22:01 ` Mark Brown
2016-10-28 12:07 ` Arnd Bergmann
2016-10-28 12:17 ` Richard Weinberger
2016-10-29 5:38 ` Paolo Valente
2016-10-29 5:38 ` Paolo Valente
2016-10-29 13:12 ` Bart Van Assche
2016-10-29 13:12 ` Bart Van Assche
2016-10-29 14:12 ` Jens Axboe
2016-10-30 3:06 ` Paolo Valente
2016-10-30 3:06 ` Paolo Valente
2016-10-26 12:37 ` Paolo Valente
2016-10-26 12:37 ` Paolo Valente
-- strict thread matches above, loose matches on Subject: below --
2016-10-30 17:48 Manuel Krause
2016-10-29 17:08 Manuel Krause
2016-10-25 8:48 Paolo Valente
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