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