[U-Boot] [U-Boot, V3, 1/3] drivers: block: add block device cache

[Tom Rini]

On Mon, Mar 28, 2016 at 10:05:44AM -0700, Eric Nelson wrote:

> Add a block device cache to speed up repeated reads of block devices by
> various filesystems.
> 
> This small amount of cache can dramatically speed up filesystem
> operations by skipping repeated reads of common areas of a block
> device (typically directory structures).
> 
> This has shown to have some benefit on FAT filesystem operations of
> loading a kernel and RAM disk, but more dramatic benefits on ext4
> filesystems when the kernel and/or RAM disk are spread across
> multiple extent header structures as described in commit fc0fc50.
> 
> The cache is implemented through a minimal list (block_cache) maintained
> in most-recently-used order and count of the current number of entries
> (cache_count). It uses a maximum block count setting to prevent copies
> of large block reads and an upper bound on the number of cached areas.
> 
> The maximum number of entries in the cache defaults to 32 and the maximum
> number of blocks per cache entry has a default of 2, which has shown to
> produce the best results on testing of ext4 and FAT filesystems.
> 
> The 'blkcache' command (enabled through CONFIG_CMD_BLOCK_CACHE) allows
> changing these values and can be used to tune for a particular filesystem
> layout.
> 
> Signed-off-by: Eric Nelson <eric at nelint.com>

Applied to u-boot/master, thanks!

-- 
Tom
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