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Diffstat (limited to 'Documentation/block/mmc-max-speed.txt')
-rw-r--r-- | Documentation/block/mmc-max-speed.txt | 38 |
1 files changed, 38 insertions, 0 deletions
diff --git a/Documentation/block/mmc-max-speed.txt b/Documentation/block/mmc-max-speed.txt new file mode 100644 index 000000000000..3f052b9fb999 --- /dev/null +++ b/Documentation/block/mmc-max-speed.txt @@ -0,0 +1,38 @@ +eMMC Block layer simulation speed controls in /sys/block/mmcblk*/ +=============================================== + +Turned on with CONFIG_MMC_SIMULATE_MAX_SPEED which enables MMC device speed +limiting. Used to test and simulate the behavior of the system when +confronted with a slow MMC. + +Enables max_read_speed, max_write_speed and cache_size attributes and module +default parameters to control the write or read maximum KB/second speed +behaviors. + +NB: There is room for improving the algorithm for aspects tied directly to +eMMC specific behavior. For instance, wear leveling and stalls from an +exhausted erase pool. We would expect that if there was a need to provide +similar speed simulation controls to other types of block devices, aspects of +their behavior are modelled separately (e.g. head seek times, heat assist, +shingling and rotational latency). + +/sys/block/mmcblk0/max_read_speed: + +Number of KB/second reads allowed to the block device. Used to test and +simulate the behavior of the system when confronted with a slow reading MMC. +Set to 0 or "off" to place no speed limit. + +/sys/block/mmcblk0/max_write_speed: + +Number of KB/second writes allowed to the block device. Used to test and +simulate the behavior of the system when confronted with a slow writing MMC. +Set to 0 or "off" to place no speed limit. + +/sys/block/mmcblk0/cache_size: + +Number of MB of high speed memory or high speed SLC cache expected on the +eMMC device being simulated. Used to help simulate the write-back behavior +more accurately. The assumption is the cache has no delay, but draws down +in the background to the MLC/TLC primary store at the max_write_speed rate. +Any write speed delays will show up when the cache is full, or when an I/O +request to flush is issued. |