On 21/09/17 12:01, Ulf Hansson wrote: > On 13 September 2017 at 13:40, Adrian Hunter <adrian.hunter@xxxxxxxxx> 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.
