On 21/09/17 12:01, Ulf Hansson wrote:

On 13 September 2017 at 13:40, Adrian Hunter [off-list ref] wrote:

quoted

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.