Re: [PATCH V8 00/14] mmc: Add Command Queue support

[Adrian Hunter]

On 20/10/17 15:30, Adrian Hunter wrote:
> On 19/10/17 14:44, Adrian Hunter wrote:
>> 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?
> 
> Still ping?

How is your silence in any way an acceptable way to execute your
responsibilities as maintainer!