On 11/10/17 15:13, Ulf Hansson wrote: > On 10 October 2017 at 15:31, Adrian Hunter <adrian.hunter@xxxxxxxxx> wrote: >> On 10/10/17 16:08, Ulf Hansson wrote: >>> [...] >>> >>>>>>> >>>>>>> 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!? >>>> >>>> MMC_CAP_WAIT_WHILE_BUSY is necessary because it means that a data transfer >>>> request has finished when the host controller calls mmc_request_done(). i.e. >>>> polling the card is not necessary. >>> >>> Well, that is a rather big change on its own. Earlier we polled with >>> CMD13 to verify that the card has moved back to the transfer state, in >>> case it was a write. And that was no matter of MMC_CAP_WAIT_WHILE_BUSY >>> was set or not. Right!? >> >> Yes >> >>> >>> I am not sure it's a good idea to bypass that validation, it seems >>> fragile to rely only on the busy detection on DAT line for writes. >> >> Can you cite something from the specifications that backs that up, because I >> couldn't find anything to suggest that CMD13 polling was expected. > > No I can't, but I don't see why that matters. > > My point is, if we want to go down that road by avoiding the CMD13 > polling, that needs to be a separate change, which we can test and > confirm on its own. > >> >>> >>>> >>>> Have you tried V9 or V10. There was a fix in V9 related to calling >>>> ->post_req() which could mess up DMA. >>> >>> I have used V10. >>> >>>> >>>> The other thing that could go wrong with DMA is if it cannot accept >>>> ->post_req() being called from mmc_request_done(). >>> >>> I don't think mmci has a problem with that, however why do you want to >>> do this? Wouldn't that defeat some of the benefits with the async >>> request mechanism? >> >> Perhaps - but it would need to be tested. If there are more requests >> waiting, one optimization could be to defer ->post_req() until after the >> next request is started. > > This is already proven, because this how the existing mmc async > request mechanism works. > > In ->post_req() callbacks, host drivers may do dma_unmap_sg(), which > is something that could be costly and therefore it's better to start a > new request before, such these things can go on in parallel. OK I will make a patch that takes care of both issues. That will also mean the request is not completed in the ->done() callback because ->post_req() must precede block layer completion. -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
