[U-Boot] [RFC V2 PATCH 0/3] Add cache for block devices

[Marek Vasut]

On 03/21/2016 02:45 AM, Eric Nelson wrote:
> Here's a more full-featured implementation of a cache for block devices
> that uses a small linked list of cache blocks.

Why do you use linked list ? You have four entries, you can as well use
fixed array. Maybe you should implement an adaptive cache would would
use the unpopulated malloc area and hash the sector number(s) into that
area ?

> Experimentation loading a 4.5 MiB kernel from the root directory of 
> a FAT filesystem shows that a single cache entry of a single block
> is the only 

only ... what ? This is where things started to be interesting, but you
leave us hanging :)

> Loading the same from the /boot directory of an ext4 filesystem
> shows a benefit with 4 cache entries, though the single biggest
> benefit is also with the first cache entry:
> 
> => for n in 0 1 2 4 8 ; do 
>>    blkc 1 $n ; blkc c ; blkc i ; 
>>    load mmc 0:2 10008000 /boot/zImage ; 
>> done
> changed to max of 0 entries of 1 blocks each
> 4955304 bytes read in 503 ms (9.4 MiB/s)
> changed to max of 1 entries of 1 blocks each
> 4955304 bytes read in 284 ms (16.6 MiB/s)
> changed to max of 2 entries of 1 blocks each
> 4955304 bytes read in 284 ms (16.6 MiB/s)
> changed to max of 4 entries of 1 blocks each
> 4955304 bytes read in 255 ms (18.5 MiB/s)
> changed to max of 8 entries of 1 blocks each
> 4955304 bytes read in 255 ms (18.5 MiB/s)
> 
> As mentioned earlier in this thread, the modification to the mmc
> layer should probably be simpler and easier to apply to other
> block subsystems.
> 
> Eric Nelson (3):
>   drivers: block: add block device cache
>   block: add Kconfig options for BLOCK_CACHE, CMD_BLOCK_CACHE
>   mmc: add support for block device cache
> 
>  drivers/block/Kconfig       |  19 ++++
>  drivers/block/Makefile      |   1 +
>  drivers/block/cache_block.c | 240 ++++++++++++++++++++++++++++++++++++++++++++
>  drivers/mmc/mmc.c           |  10 +-
>  drivers/mmc/mmc_write.c     |   7 ++
>  include/part.h              |  69 +++++++++++++
>  6 files changed, 345 insertions(+), 1 deletion(-)
>  create mode 100644 drivers/block/cache_block.c
> 


-- 
Best regards,
Marek Vasut