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
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