> -----Original Message----- > From: Adrian Hunter [mailto:adrian.hunter@xxxxxxxxx] > Sent: Monday, September 20, 2010 5:20 PM > To: Ghorai, Sukumar > Cc: linux-mmc@xxxxxxxxxxxxxxx; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; > Adrian Hunter > Subject: Re: [PATCH] mmc: failure of block read wait for long time > > On 20/09/10 11:57, Ghorai, Sukumar wrote: > > Adrian, > > > >> -----Original Message----- > >> From: Adrian Hunter [mailto:adrian.hunter@xxxxxxxxx] > >> Sent: Monday, September 20, 2010 1:24 PM > >> To: Ghorai, Sukumar > >> Cc: linux-mmc@xxxxxxxxxxxxxxx; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; > >> Adrian Hunter > >> Subject: Re: [PATCH] mmc: failure of block read wait for long time > >> > >> On 14/09/10 08:15, ext Ghorai, Sukumar wrote: > >>> Adrian, > >>> > >>> [..snip..] > >>>>>>> [Ghorai] Adrian, > >>>>>>> Yes this works and reduced the retry by 1/4 (2048 to 512 times for > >> 1MB > >>>>>> data read) form the original code; > >>>>>>> Initially it was retrying for each page(512 bytes) after multi- > block > >>>>>> read fail; but this solution is retying for each segment(2048 > bytes); > >>>>>>> 1. Now say block layrer reading 1MB and failed for the 1st segment. > >> So > >>>>>> it will still retry for 1MB/2048-bytes, i.e. 512 times. > >>>>>>> 2. So do you think any good reason to retry again and again? > >>>>>> If you have 1MB that is not readable, it sounds like the card is > >> broken. > >>>>>> Why are so many reads failing? Has the card been removed? > >>>>>> > >>>>>> You might very rarely see ECC errors in a small number of sectors, > >>>>>> but more than that sounds like something else is broken. > >>>>> > >>>>> [Ghorai] yes, one example is we remove the card when reading data, > >>>> > >>>> Well, that is a different case. Once the card has gone, the block > >> driver > >>>> can (and will once the remove method is called) error out all I/O > >>>> requests without sending them to MMC. That doesn't happen until > there > >>>> is a card detect interrupt and a resulting rescan. > >>> > >>> [Ghorai] here we are discussing two problem, > >>> 1. If IO failed how to stop retry; because of - > >>> a. internal card error > >>> b. issue in Filesystem, driver, or host controller issue > >>> c. or cards removed. > >>> > >>> 2. And 2nd how to sync block-layer IO, if card removed, > >>> a. case 1: when card removed interrupt support by the platform > >>> b. case 2: when card removed interrupt does not support by the > >> platform? > >>> > >>>> > >>>> A possible solution is to put a flag on mmc_card to indicate > card_gone > >>>> that gets set as soon as the drivers card detect interrupt shows > there > >>>> is no card (hoping that we are not getting any bouncing on card > detect) > >>>> and then have mmc_wait_for_req() simple return -ENODEV immediately if > >>>> the card_gone flag is set. Finally, if the mmc block driver sees > >>>> a -ENODEV error, it should also check the card_gone flag (via a new > >>>> core function) and if the card is gone, do not retry - and perhaps > >>>> even error out the rest of the I/O request queue as well. > >>> > >>> [Ghorai] your idea address the 2.a case, but not 2.b, 1.a, 1.b > >> > >> The card removal case can be extended to use the bus ops detect method > >> when there is no card detect irq. I will send a RFC patch. > >> > >> With respect to 1.a: > >> - If the card has an internal error, then it is broken. The user > >> should remove the card and use a better one. I do not see how > reducing > >> retry delays really helps the user very much. Arguably if the card > >> becomes unresponsive, the MMC core could provide a facility to > >> reinitialise the card, but that is yet another issue. > >> > >> With respect to 1.b: > >> - The file system cannot cause the block driver to have I/O errors. > >> - If there are errors in the driver they should be fixed. > >> - If there are hardware problems with the host controller, then > >> it is up to the host controller driver to deal with them e.g. > >> by resetting the controller. I don't see what this has to do with > >> the block driver. > >> > >> You leave out the important case of ECC errors. I am concerned about > >> this because of the possibility that it happens inside a file system > >> journal e.g. EXT4 journal. Perhaps the journal may be recovered if the > >> error only affects the last transaction, but perhaps not if it destroys > >> other transactions - which could happen if the approach you suggest > >> is taken. > >> > > [Ghorai] Thanks lot for your descriptive answer. > > 1. Can you answer this? 2.b. case 2: when card removed interrupt does > not support by the platform? > > As I wrote above: The card removal case can be extended to use the bus ops > detect method when there is no card detect irq. I will send a RFC patch. > > > > > 2. Why block layer handling for inter-leave data? Can you give example > diver who is returning interleave data? And how to tell application that > buffer having interleave data? > > I am not sure what you mean by interleave data, but file systems for > example > are free to map any block to any file, directory or file system object, > so a consecutive series of sectors may contain unrelated data. Up to a > maximum > size, the block layer merges I/O requests when the sectors are consecutive, > so an I/O request can also contain unrelated data. [Ghorai] 1. I don't think so, FS know where data exists and where is the free space. Except oth cluster. 2. Where its mentioned in block media that for segment-x[i],x[j] data read fail out of all all requested segments form [1..n]. And I never gone through any driver/protocol, that retry the next i+1th segment where ith-segment is failed. And for that my suggestion is preferred. > > > > >>> > >>> And the solution I was proposing to return the status of IO failure as > >> soon as possible to above layer; and handle the card removed interrupt > >> separately or any other issue in h/w or s/w or combination of both. Or > >> just think again when platform don't have the card remove interrupt. > >>> > >>> So my patch addresses the 1st part > >> > >> It is absolutely unacceptable to return I/O errors to the upper layers > >> for segments that do not have errors. > >> > >>> And for the 2nd part we can submit the patch anytime. > >>> > >>>> > >>>> I can suggest a patch if you want but I am on vacation next week so > >>>> it will have to wait a couple of weeks. > >>>> > >>>>> And moreover we should not give the interleave data to apps, as we > >> don't > >>>> have option to tell application for the valid data. > >>>>> > >>> [..snip..] > >>> http://comments.gmane.org/gmane.linux.kernel.mmc/2714 > >>> > >>>>> > >>> > >>> > > > > -- > > 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 > > -- 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
