RE: [PATCH v3] mmc: rtsx: improve performance for multi block rw

[Ricky WU <ricky_wu@realtek.com>]

Hi Ulf Hansson,

Can I know what is this patch status or has some concern on this patch?

Ricky
> -----Original Message-----
> From: Ulf Hansson <ulf.hansson@linaro.org>
> Sent: Thursday, February 10, 2022 10:57 PM
> To: Ricky WU <ricky_wu@realtek.com>
> Cc: tommyhebb@gmail.com; linux-mmc@vger.kernel.org;
> linux-kernel@vger.kernel.org
> Subject: Re: [PATCH v3] mmc: rtsx: improve performance for multi block rw
> 
> On Thu, 10 Feb 2022 at 07:43, Ricky WU <ricky_wu@realtek.com> wrote:
> >
> >
> >
> > > -----Original Message-----
> > > From: Ulf Hansson <ulf.hansson@linaro.org>
> > > Sent: Monday, February 7, 2022 7:11 PM
> > > To: Ricky WU <ricky_wu@realtek.com>
> > > Cc: tommyhebb@gmail.com; linux-mmc@vger.kernel.org;
> > > linux-kernel@vger.kernel.org
> > > Subject: Re: [PATCH v3] mmc: rtsx: improve performance for multi
> > > block rw
> > >
> > > [...]
> > >
> > > > > > > >
> > > > > > > > Do you have any suggestion for testing random I/O But we
> > > > > > > > think random I/O will not change much
> > > > > > >
> > > > > > > I would probably look into using fio,
> > > > > > > https://fio.readthedocs.io/en/latest/
> > > > > > >
> > > > > >
> > > > > > Filled random I/O data
> > > > > > Before the patch:
> > > > > > CMD (Randread):
> > > > > > sudo fio -filename=/dev/mmcblk0 -direct=1 -numjobs=1 -thread
> > > > > > -group_reporting -ioengine=psync -iodepth=1 -size=1G
> > > > > > -name=mytest -bs=1M -rw=randread
> > > > >
> > > > > Thanks for running the tests! Overall, I would not expect an
> > > > > impact on the throughput when using a big blocksize like 1M.
> > > > > This is also pretty clear from the result you have provided.
> > > > >
> > > > > However, especially for random writes and reads, we want to try
> > > > > with smaller blocksizes. Like 8k or 16k, would you mind running
> > > > > another round of tests to see how that works out?
> > > > >
> > > >
> > > > Filled random I/O data(8k/16k)
> > >
> > > Hi Ricky,
> > >
> > > Apologize for the delay! Thanks for running the tests. Let me
> > > comment on them below.
> > >
> > > >
> > > > Before(randread)
> > > > 8k:
> > > > Cmd: sudo fio -filename=/dev/mmcblk0 -direct=1 -numjobs=1 -thread
> > > > -group_reporting -ioengine=psync -iodepth=1 -size=1G -name=mytest
> > > > -bs=8k -rw=randread
> > > > mytest: (g=0): rw=randread, bs=(R) 8192B-8192B, (W) 8192B-8192B,
> > > > (T) 8192B-8192B, ioengine=psync, iodepth=1
> > > > result:
> > > > Run status group 0 (all jobs):
> > > >    READ: bw=16.5MiB/s (17.3MB/s), 16.5MiB/s-16.5MiB/s
> > > > (17.3MB/s-17.3MB/s), io=1024MiB (1074MB), run=62019-62019msec
> Disk
> > > stats (read/write):
> > > >   mmcblk0: ios=130757/0, merge=0/0, ticks=57751/0, in_queue=57751,
> > > > util=99.89%
> > > >
> > > > 16k:
> > > > Cmd: sudo fio -filename=/dev/mmcblk0 -direct=1 -numjobs=1 -thread
> > > > -group_reporting -ioengine=psync -iodepth=1 -size=1G -name=mytest
> > > > -bs=16k -rw=randread
> > > > mytest: (g=0): rw=randread, bs=(R) 16.0KiB-16.0KiB, (W)
> > > > 16.0KiB-16.0KiB, (T) 16.0KiB-16.0KiB, ioengine=psync, iodepth=1
> > > > result:
> > > > Run status group 0 (all jobs):
> > > >    READ: bw=23.3MiB/s (24.4MB/s), 23.3MiB/s-23.3MiB/s
> > > > (24.4MB/s-24.4MB/s), io=1024MiB (1074MB), run=44034-44034msec
> Disk
> > > stats (read/write):
> > > >   mmcblk0: ios=65333/0, merge=0/0, ticks=39420/0, in_queue=39420,
> > > > util=99.84%
> > > >
> > > > Before(randrwrite)
> > > > 8k:
> > > > Cmd: sudo fio -filename=/dev/mmcblk0 -direct=1 -numjobs=1 -thread
> > > > -group_reporting -ioengine=psync -iodepth=1 -size=100M
> > > > -name=mytest -bs=8k -rw=randwrite
> > > > mytest: (g=0): rw=randwrite, bs=(R) 8192B-8192B, (W) 8192B-8192B,
> > > > (T) 8192B-8192B, ioengine=psync, iodepth=1
> > > > result:
> > > > Run status group 0 (all jobs):
> > > >   WRITE: bw=4060KiB/s (4158kB/s), 4060KiB/s-4060KiB/s
> > > > (4158kB/s-4158kB/s), io=100MiB (105MB), run=25220-25220msec Disk
> > > > stats
> > > (read/write):
> > > >   mmcblk0: ios=51/12759, merge=0/0, ticks=80/24154,
> > > > in_queue=24234, util=99.90%
> > > >
> > > > 16k:
> > > > Cmd: sudo fio -filename=/dev/mmcblk0 -direct=1 -numjobs=1 -thread
> > > > -group_reporting -ioengine=psync -iodepth=1 -size=100M
> > > > -name=mytest -bs=16k -rw=randwrite
> > > > mytest: (g=0): rw=randwrite, bs=(R) 16.0KiB-16.0KiB, (W)
> > > > 16.0KiB-16.0KiB, (T) 16.0KiB-16.0KiB, ioengine=psync, iodepth=1
> > > > result:
> > > > Run status group 0 (all jobs):
> > > >   WRITE: bw=7201KiB/s (7373kB/s), 7201KiB/s-7201KiB/s
> > > > (7373kB/s-7373kB/s), io=100MiB (105MB), run=14221-14221msec Disk
> > > > stats
> > > (read/write):
> > > >   mmcblk0: ios=51/6367, merge=0/0, ticks=82/13647, in_queue=13728,
> > > > util=99.81%
> > > >
> > > >
> > > > After(randread)
> > > > 8k:
> > > > Cmd: sudo fio -filename=/dev/mmcblk0 -direct=1 -numjobs=1 -thread
> > > > -group_reporting -ioengine=psync -iodepth=1 -size=1G -name=mytest
> > > > -bs=8k -rw=randread
> > > > mytest: (g=0): rw=randread, bs=(R) 8192B-8192B, (W) 8192B-8192B,
> > > > (T) 8192B-8192B, ioengine=psync, iodepth=1
> > > > result:
> > > > Run status group 0 (all jobs):
> > > >    READ: bw=12.4MiB/s (13.0MB/s), 12.4MiB/s-12.4MiB/s
> > > > (13.0MB/s-13.0MB/s), io=1024MiB (1074MB), run=82397-82397msec
> Disk
> > > stats (read/write):
> > > >   mmcblk0: ios=130640/0, merge=0/0, ticks=74125/0, in_queue=74125,
> > > > util=99.94%
> > > >
> > > > 16k:
> > > > Cmd: sudo fio -filename=/dev/mmcblk0 -direct=1 -numjobs=1 -thread
> > > > -group_reporting -ioengine=psync -iodepth=1 -size=1G -name=mytest
> > > > -bs=16k -rw=randread
> > > > mytest: (g=0): rw=randread, bs=(R) 16.0KiB-16.0KiB, (W)
> > > > 16.0KiB-16.0KiB, (T) 16.0KiB-16.0KiB, ioengine=psync, iodepth=1
> > > > result:
> > > > Run status group 0 (all jobs):
> > > >    READ: bw=20.0MiB/s (21.0MB/s), 20.0MiB/s-20.0MiB/s
> > > > (21.0MB/s-21.0MB/s), io=1024MiB (1074MB), run=51076-51076msec
> Disk
> > > stats (read/write):
> > > >   mmcblk0: ios=65282/0, merge=0/0, ticks=46255/0, in_queue=46254,
> > > > util=99.87%
> > > >
> > > > After(randwrite)
> > > > 8k:
> > > > Cmd: sudo fio -filename=/dev/mmcblk0 -direct=1 -numjobs=1 -thread
> > > > -group_reporting -ioengine=psync -iodepth=1 -size=100M
> > > > -name=mytest -bs=8k -rw=randwrite
> > > > mytest: (g=0): rw=randwrite, bs=(R) 8192B-8192B, (W) 8192B-8192B,
> > > > (T) 8192B-8192B, ioengine=psync, iodepth=1
> > > > result:
> > > > Run status group 0 (all jobs):
> > > >   WRITE: bw=4215KiB/s (4317kB/s), 4215KiB/s-4215KiB/s
> > > > (4317kB/s-4317kB/s), io=100MiB (105MB), run=24292-24292msec Disk
> > > > stats
> > > (read/write):
> > > >   mmcblk0: ios=52/12717, merge=0/0, ticks=86/23182,
> > > > in_queue=23267, util=99.92%
> > > >
> > > > 16k:
> > > > Cmd: sudo fio -filename=/dev/mmcblk0 -direct=1 -numjobs=1 -thread
> > > > -group_reporting -ioengine=psync -iodepth=1 -size=100M
> > > > -name=mytest -bs=16k -rw=randwrite
> > > > mytest: (g=0): rw=randwrite, bs=(R) 16.0KiB-16.0KiB, (W)
> > > > 16.0KiB-16.0KiB, (T) 16.0KiB-16.0KiB, ioengine=psync, iodepth=1
> > > > result:
> > > > Run status group 0 (all jobs):
> > > >   WRITE: bw=6499KiB/s (6655kB/s), 6499KiB/s-6499KiB/s
> > > > (6655kB/s-6655kB/s), io=100MiB (105MB), run=15756-15756msec Disk
> > > > stats
> > > (read/write):
> > > >   mmcblk0: ios=51/6347, merge=0/0, ticks=84/15120, in_queue=15204,
> > > > util=99.80%
> > >
> > > It looks like the rand-read tests above are degrading with the new
> > > changes, while rand-writes are both improving and degrading.
> > >
> > > To summarize my view from all the tests you have done at this point
> > > (thanks a lot); it looks like the block I/O merging isn't really
> > > happening at common blocklayer, at least to that extent that would
> > > benefit us. Clearly you have shown that by the suggested change in
> > > the mmc host driver, by detecting whether the "next" request is
> > > sequential to the previous one, which allows us to skip a
> > > CMD12 and minimize some command overhead.
> > >
> > > However, according to the latest tests above, you have also proved
> > > that the changes in the mmc host driver doesn't come without a cost.
> > > In particular, small random-reads would degrade in performance from
> > > these changes.
> > >
> > > That said, it looks to me that rather than trying to improve things
> > > for one specific mmc host driver, it would be better to look at this
> > > from the generic block layer point of view - and investigate why
> > > sequential reads/writes aren't getting merged often enough for the
> > > MMC/SD case. If we can fix the problem there, all mmc host drivers would
> benefit I assume.
> > >
> >
> > So you are thinking about how to patch this in MMC/SD?
> > I don't know if this method is compatible with other MMC Hosts? Or
> > they need to patch other code on their host driver
> 
> I would not limit this to the core layer of MMC/SD. The point I was trying to
> make was that it doesn't look like the generic block layer is merging the
> sequential I/O requests in the most efficient way, at least for the eMMC/SD
> devices. Why this is the case, I can't tell. It looks like we need to do some more
> in-depth analysis to understand why merging isn't efficient for us.
> 
> >
> > > BTW, have you tried with different I/O schedulers? If you haven't
> > > tried BFQ, I suggest you do as it's a good fit for MMC/SD.
> > >
> >
> > I don’t know what is different I/O schedulers means?
> 
> What I/O scheduler did you use when running the test?
> 
> For MMC/SD the only one that makes sense to use is BFQ, however that needs
> to be configured via sysfs after boot. There is no way, currently, to make it the
> default, I think. You may look at Documentation/block/bfq-iosched.rst, if you
> are more interested.
> 
> Kind regards
> Uffe
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