| 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. |
