Re: Grub2 EFI: Image loading from USB takes too long

["Vladimir 'φ-coder/phcoder' Serbinenko" <phcoder@gmail.com>]

On 05.04.2011 07:33, Aravind Srinivasan wrote:
> include/grub/disk.h
> <snip>
> /* The size of a disk cache in sector units.  */
> #define GRUB_DISK_CACHE_SIZE   8
> #define GRUB_DISK_CACHE_BITS   3
> <snip>
>
> I tried changing this value to 8192 - and the time it took to load the same
> image came down to 10 secs !
> /* The size of a disk cache in sector units.  */
> #define GRUB_DISK_CACHE_SIZE   8192
> #define GRUB_DISK_CACHE_BITS   13
>
> I am not sure of the reason for setting the cache size to a low value and any
> possible issues in increasing this size. Appreciate any input on this.
This value is a misnomer. It's not a cache size but a cache unit size. 
As immediate effect it has that if one reads a single 512B, sector one 
reads an entire block of 4K. Under normal conditions values of around 
32K-128K (6-8/64-256) would be optimal. It seems that some EFI 
implementations do a "buffering" only to discard the buffered data. Some 
of the reports suggest that this braindamage is limited to disk io and 
doesn't happen with Block IO. Values you propose would result in 4M 
reads even when one needs just few sectors and so is suboptimal under 
normal conditions.
I'll prepare few patches to investigate.
After 1.99 the GRUB_DISK_CACHE_BITS will be increased to 6-8 range 
since, it's optimal and my AF support requires sector size to be smaller 
than cache unit size.

-- 
Regards
Vladimir 'φ-coder/phcoder' Serbinenko