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 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 Technologies, Yejin Moon, Jae Hoon Chung from Samsung and others. ---- v1 -> v2:- * Convert threshold for hpi usage to a tuning parameter (sysfs) * Add Documentation/ABI for all sysfs entries * Add implementation of abort for OMAP controller * Rebased to 3.4-rc4 + mmc-next 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-hpiv2 ---------------------------------------------------------------- Ilan Smith (3): FS: Added demand paging markers to filesystem MM: Added page swapping markers to memory management block: treat DMPG and SWAPIN requests as special Venkatraman S (13): block: add queue attributes to manage dpmg and swapin requests block: add sysfs attributes for runtime control of dpmg and swapin block: Documentation: add sysfs ABI for expedite_dmpg and expedite_swapin 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: Implement foreground request preemption procedure mmc: sysfs: Add sysfs entry for tuning preempt_time_threshold mmc: Documentation: Add sysfs ABI for hpi_time_threshold mmc: block: Implement HPI invocation and handling logic. mmc: Update preempted request with CORRECTLY_PRG_SECTORS_NUM info mmc: omap_hsmmc: Implement abort_req host_ops Documentation/ABI/testing/sysfs-block | 12 ++ Documentation/ABI/testing/sysfs-devices-mmc | 12 ++ block/blk-core.c | 18 +++ block/blk-sysfs.c | 16 +++ block/elevator.c | 14 ++- drivers/mmc/card/block.c | 143 ++++++++++++++++++++-- drivers/mmc/card/queue.h | 1 + drivers/mmc/core/core.c | 67 ++++++++++ drivers/mmc/core/mmc.c | 25 ++++ drivers/mmc/host/omap_hsmmc.c | 55 ++++++++- fs/mpage.c | 2 + include/linux/bio.h | 8 ++ include/linux/blk_types.h | 4 + include/linux/blkdev.h | 8 ++ include/linux/mmc/card.h | 1 + include/linux/mmc/core.h | 19 +++ include/linux/mmc/host.h | 1 + include/linux/mmc/mmc.h | 4 + mm/page_io.c | 3 +- 19 files changed, 395 insertions(+), 18 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
