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

[Eric Nelson <eric@nelint.com>]

Hi Tom,

On 04/01/2016 06:59 PM, Tom Rini wrote:
> 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@nelint.com>
> 
> Applied to u-boot/master, thanks!
> 

Whoops. I have a couple of minor updates from Stephen's last review that
I'll forward shortly.