Here's an example of a very simple cache for block devices that will prevent duplicate back-to-back reads from the same block device.
By itself, this is sufficient to speed reads of certain files from ext4 by 30x as described in this thread.
The areas I think could benefit most from some level of block cache in U-Boot are: - reads from partition tables - directory searches
Having more than one cache entry is probably better for both of those, but I'd like to get some feedback first.
The implementation explicitly prevents reads of more than 8 blocks to prevent slowing down the most speed-critical operations (reading files) and I'm not sure this is the right choice of size.
The small size limit also prevents the overhead in the interface to cache_block_fill() from being a problem. A more robust approach would allow the cache to take over previously allocated blocks, but this would also be more invasive, since some cacheable blocks are currently allocated on the stack.
Eric Nelson (2): add block device cache mmc: add support for block device cache
drivers/block/Makefile | 1 + drivers/block/cache_block.c | 76 +++++++++++++++++++++++++++++++++++++++++++++ drivers/mmc/mmc.c | 10 +++++- drivers/mmc/mmc_write.c | 7 +++++ include/part.h | 65 ++++++++++++++++++++++++++++++++++++++ 5 files changed, 158 insertions(+), 1 deletion(-) create mode 100644 drivers/block/cache_block.c