On Thu, Feb 17, 2011 at 9:47 AM, Arnd Bergmann <arnd@xxxxxxxx> wrote: > I think I'd try to reduce the number of sysfs files needed for this. > What are the values you would typically set here? > > My feeling is that separating unaligned page writes from full pages > or multiples of pages could always be benefitial for all cards, or at > least harmless, but that will require more measurements. > Whether to do the reliable write or not could be a simple flag > if the numbers are the same. I thought about this some more, and I realized it would be ugly if everybody added enable_workaround_sec_start/enable_workaround_sec_end for every novel idea of working around some issue with performance/reliability on mmc/sd cards. What about letting the user/embedder create policies for how certain accesses are done? That way you give runtime-accessible blocks for tuning mmc block layer while having one interface to manipulate (and combine) multiple workarounds, all the while catching conflicts and without forcing specific policy in code. Essentially under /sys/block/mmcblk0/device you have an attribute called "policies". Example: # echo mypol0 > /sys/block/mmcblk0/device/policies # ls /sys/block/mmcblk0/device/mypol0 debug delete start_block end_block access_size_low access_size_high write_policy erase_policy read_policy # cat /sys/block/mmcblk0/device/mypol0/write_policy Current: none 0x00000001: Split unaligned writes across page_size 0x00000002: Split writes into page_size chunks and write using reliable writes 0x00000004: Use reliable writes for WRITE_META blocks. # cat /sys/block/mmcblk0/device/mypol0/erase_policy Current: none 0x00000001: Use secure erase. # echo 1 > delete # Policy is deleted. The policies are all stored in a rb-tree. First order of business inside mmc_blk_issue_rw_rq/mmc_blk_issue_* is to fetch an existing policy given the access type and block start/end (which both tells where the access is going and the size of the access). Later, it's that policy information which controls how the request is translated into MMC commands. I'm almost done with a prototype. I noticed that all sysfs attributes are managed by code under core/mmc.c and core/sd.c, duplicating where necessary. I think some of the new block-related settings like page_size (or policies) are generic enough that they should live in the card/block code. How about putting all future sysfs block related things into block-sysfs.c? Thanks, A -- 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
