drivers: block: add block device cache

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@nelint.com>

1 files changed, 11 insertions, 0 deletions

diff --git a/cmd/Kconfig b/cmd/Kconfig
index cdcaff8..fe8b4f0 100644
--- a/cmd/Kconfig
+++ b/cmd/Kconfig
@@ -497,6 +497,17 @@ config SYS_AMBAPP_PRINT_ON_STARTUP
 	help
 	  Show AMBA Plug-n-Play information on startup.
 
+config CMD_BLOCK_CACHE
+	bool "blkcache - control and stats for block cache"
+	depends on BLOCK_CACHE
+	default y if BLOCK_CACHE
+	help
+	  Enable the blkcache command, which can be used to control the
+	  operation of the cache functions.
+	  This is most useful when fine-tuning the operation of the cache
+	  during development, but also allows the cache to be disabled when
+	  it might hurt performance (e.g. when using the ums command).
+
 config CMD_TIME
 	bool "time"
 	help