> Using the disk supplied data about where the error occurred (provided > the disk returns it) eliminates all the readahead problems like the one ATA disks do provide sector information generally, as do CD-ROMs, in fact we actually decode it for error reporting so probably all the bits are there to improve any reporting for most read side cases. >From some of the traces I have been debugging I am not convinced the scsi mid layer does the right thing any more. It uses to be handling CD-R media (where the end of media is not well defined) but nowdays seems to be reporting errors even when told that the I/O partly succeeded. I need to debug that case further however but as I don't have one of the problem drives its a bit tricky. > above. Perhaps just turning of readahead for disks that don't supply > error location information would be a reasonable workaround? Not really. From a performance perspective Mark's patch is vastly superior because it punishes the incredibly rare error case not the routine working performance. Avoiding the need to do either would be even better - as would fixing the block layer not to mess up retries in this situation. For low speed devices like MMC cards and flash it might make sense not to merge unrelated requests however so that only the relevant one fails. Alan -- To unsubscribe from this list: send the line "unsubscribe linux-ide" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
