On 18/10/17 09:16, Adrian Hunter wrote: > On 11/10/17 16:58, Ulf Hansson wrote: >> On 11 October 2017 at 14:58, Adrian Hunter <adrian.hunter@xxxxxxxxx> wrote: >>> 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. >> >> Right. >> >> Actually completing the request in the ->done callback, may still be >> possible, because in principle it only needs to inform the other >> prepared request that it may start, before it continues to post >> process/completes the current one. >> >> However, by looking at for example how mmci.c works, it actually holds >> its spinlock while it calls mmc_request_done(). The same spinlock is >> taken in the ->request() function, but not in the ->post_req() >> function. In other words, completing the request in the ->done() >> callback, would make mmci to keep the spinlock held throughout the >> post processing cycle, which then prevents the next request from being >> started. >> >> So my conclusion is, let's start a as you suggested, by not completing >> the request in ->done() as to maintain existing behavior. Then we can >> address optimizations on top, which very likely will involve doing >> changes to host drivers as well. > > Have you tested the latest version now? > Ping? -- 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
