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SubjectRe: [PATCH V8 00/14] mmc: Add Command Queue support
On 21 September 2017 at 11:44, Adrian Hunter <adrian.hunter@intel.com> wrote:
> On 21/09/17 12:01, Ulf Hansson wrote:
>> On 13 September 2017 at 13:40, Adrian Hunter <adrian.hunter@intel.com> wrote:
>>> Hi
>>>
>>> Here is V8 of the hardware command queue patches without the software
>>> command queue patches, now using blk-mq and now with blk-mq support for
>>> non-CQE I/O.
>>>
>>> After the unacceptable debacle of the last release cycle, I expect an
>>> immediate response to these patches.
>>>
>>> HW CMDQ offers 25% - 50% better random multi-threaded I/O. I see a slight
>>> 2% drop in sequential read speed but no change to sequential write.
>>>
>>> Non-CQE blk-mq showed a 3% decrease in sequential read performance. This
>>> seemed to be coming from the inferior latency of running work items compared
>>> with a dedicated thread. Hacking blk-mq workqueue to be unbound reduced the
>>> performance degradation from 3% to 1%.
>>>
>>> While we should look at changing blk-mq to give better workqueue performance,
>>> a bigger gain is likely to be made by adding a new host API to enable the
>>> next already-prepared request to be issued directly from within ->done()
>>> callback of the current request.
>>
>> Adrian, I am reviewing this series, however let me comment on each
>> change individually.
>>
>> I have also run some test on my ux500 board and enabling the blkmq
>> path via the new MMC Kconfig option. My idea was to run some iozone
>> comparisons between the legacy path and the new blkmq path, but I just
>> couldn't get to that point because of the following errors.
>>
>> I am using a Kingston 4GB SDHC card, which is detected and mounted
>> nicely. However, when I decide to do some writes to the card I get the
>> following errors.
>>
>> root@ME:/mnt/sdcard dd if=/dev/zero of=testfile bs=8192 count=5000 conv=fsync
>> [ 463.714294] mmci-pl18x 80126000.sdi0_per1: error during DMA transfer!
>> [ 464.722656] mmci-pl18x 80126000.sdi0_per1: error during DMA transfer!
>> [ 466.081481] mmci-pl18x 80126000.sdi0_per1: error during DMA transfer!
>> [ 467.111236] mmci-pl18x 80126000.sdi0_per1: error during DMA transfer!
>> [ 468.669647] mmci-pl18x 80126000.sdi0_per1: error during DMA transfer!
>> [ 469.685699] mmci-pl18x 80126000.sdi0_per1: error during DMA transfer!
>> [ 471.043334] mmci-pl18x 80126000.sdi0_per1: error during DMA transfer!
>> [ 472.052337] mmci-pl18x 80126000.sdi0_per1: error during DMA transfer!
>> [ 473.342651] mmci-pl18x 80126000.sdi0_per1: error during DMA transfer!
>> [ 474.323760] mmci-pl18x 80126000.sdi0_per1: error during DMA transfer!
>> [ 475.544769] mmci-pl18x 80126000.sdi0_per1: error during DMA transfer!
>> [ 476.539031] mmci-pl18x 80126000.sdi0_per1: error during DMA transfer!
>> [ 477.748474] mmci-pl18x 80126000.sdi0_per1: error during DMA transfer!
>> [ 478.724182] mmci-pl18x 80126000.sdi0_per1: error during DMA transfer!
>>
>> I haven't yet got the point of investigating this any further, and
>> unfortunate I have a busy schedule with traveling next week. I will do
>> my best to look into this as soon as I can.
>>
>> Perhaps you have some ideas?
>
> The behaviour depends on whether you have MMC_CAP_WAIT_WHILE_BUSY. Try
> changing that and see if it makes a difference.

Yes, it does! I disabled MMC_CAP_WAIT_WHILE_BUSY (and its
corresponding code in mmci.c) and the errors goes away.

When I use MMC_CAP_WAIT_WHILE_BUSY I get these problems:

[ 223.820983] mmci-pl18x 80126000.sdi0_per1: error during DMA transfer!
[ 224.815795] mmci-pl18x 80126000.sdi0_per1: error during DMA transfer!
[ 226.034881] mmci-pl18x 80126000.sdi0_per1: error during DMA transfer!
[ 227.112884] mmci-pl18x 80126000.sdi0_per1: error during DMA transfer!
[ 227.220275] mmc0: Card stuck in wrong state! mmcblk0 mmc_blk_card_stuck
[ 228.686798] mmci-pl18x 80126000.sdi0_per1: error during DMA transfer!
[ 229.892150] mmci-pl18x 80126000.sdi0_per1: error during DMA transfer!
[ 231.031890] mmci-pl18x 80126000.sdi0_per1: error during DMA transfer!
[ 232.239013] mmci-pl18x 80126000.sdi0_per1: error during DMA transfer!
5000+0 records in
5000+0 records out
root@ME:/mnt/sdcard

I looked at the new blkmq code from patch v10 13/15. It seems like the
MMC_CAP_WAIT_WHILE_BUSY is used to determine whether the async request
mechanism should be used or not. Perhaps I didn't looked close enough,
but maybe you could elaborate on why this seems to be the case!?

Kind regards
Uffe

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