(This is still work in progress. Posting for early review and suggestions) Standard eMMC (Embedded MultiMedia Card) specification expects to execute one request at a time. If some requests are more important than others, they can't be aborted while the flash procedure is in progress. New versions of the eMMC standard (4.41 and above) specfies a feature called High Priority Interrupt (HPI). This enables an ongoing transaction to be aborted using a special command (HPI command) so that the card is ready to receive new commands immediately. Then the new request can be submitted to the card, and optionally the interrupted command can be resumed again. Some restrictions exist on when and how the command can be used. For example, only write and write-like commands (ERASE) can be preempted, and the urgent request must be a read. In order to support this in software, a) At the top level, some policy decisions have to be made on what is worth preempting for. This implementation uses the demand paging requests and swap read requests as potential reads worth preempting an ongoing long write. This is expected to provide improved responsiveness for smarphones with multitasking capabilities - example would be launch a email application while a video capture session (which causes long writes) is ongoing. b) At the block handler, the higher priority request should be queued ahead of the pending requests in the elevator c) At the MMC block and core level, transactions have to executed to enforce the rules of the MMC spec and make a reasonable tradeoff if the ongoing command is really worth preempting. (For example, is it too close to completing already ?). The current implementation uses a fixed time logic. If 10ms has already elapsed since the first request was submitted, then a new high priority request would not cause a HPI, as it is expected that the first request would finish soon. Further work is needed to dynamically tune this value (maybe through sysfs) or automatically determine based on average write times of previous requests. d) At the lowest level (MMC host controllers), support interface to provide a transition path for ongoing transactions to be aborted and the controller to be ready to receive next command. More information about this feature can be found at Jedec Specification:- http://www.jedec.org/standards-documents/docs/jesd84-a441 Presentation on eMMC4.41 features:- http://www.jedec.org/sites/.default/files/Victor_Tsai.pdf Still TODO:- * Provide sysfs entry for tuning the threshold time for preemption * Implement resuming of the preempted request by checking CORRECTLY_PROGRAMMED_SECTORS_NUM field. * Provide implementation of abort_req for omap_hsmmc_driver (This is almost done, needs a few tests) Acknowledgements:- In no particular order, thanks to Arnd Bergmann and Saugata Das from Linaro, Ilan Smith and Alex Lemberg from Sandisk, Luca Porzio from Micron devices, Yejin Moon, Jae Hoon Chung from Samsung and others. ---- This patch series depends on a few other related cleanups in MMC driver. All the patches and the dependent series can be pulled from git://github.com/svenkatr/linux.git my/mmc/3.4/foreground-hpiv1 Ilan Smith (3): fs: Add demand paging markers to filesystem mm: Add page swapping markers to memory management block: Expedite DMPG and SWAPIN requests ahead of the queue Venkatraman S (8): block: Add queue attributes to manage dpmg and swapin requests mmc: Add BKOPS field offsets mmc: core: Helper function for finding preemptible command mmc: core: add preemptibility tracking fields to mmc command mmc: core: Add MMC abort interface mmc: block: Detect HPI support in card and host controller mmc: core: Utility function for mmc preemption sequence mmc: block: Implement HPI invocation and handling for foreground requests block/blk-core.c | 18 ++++++ block/blk-sysfs.c | 16 ++++++ drivers/mmc/card/block.c | 138 ++++++++++++++++++++++++++++++++++++++++----- drivers/mmc/card/queue.h | 1 + drivers/mmc/core/core.c | 28 +++++++++ fs/mpage.c | 2 + include/linux/bio.h | 8 +++ include/linux/blk_types.h | 4 ++ include/linux/blkdev.h | 8 +++ include/linux/mmc/core.h | 19 +++++++ include/linux/mmc/host.h | 1 + include/linux/mmc/mmc.h | 2 + mm/page_io.c | 3 +- 13 files changed, 233 insertions(+), 15 deletions(-) -- 1.7.10.rc2 -- 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
