Re: [PATCH 2/2] disk: increase sector size up to 127 for LBA reads

[Glenn Washburn]

On Fri,  7 Jul 2023 00:39:48 +0300
ValdikSS via Grub-devel <grub-devel@gnu.org> wrote:

> According to Wikipedia and various sources, the recommended
> value for LBA read using IBM/MS INT13 Extensions is 127 sectors.

Please cite references. I'm not seeing that on Wikipedia or osdev.org.
I do see where Wikipedia says that some Phoenix bioses are limited to a
maximum of 127 sectors, but I'm not sure that's a recommendation.

> ---
>  include/grub/disk.h | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/include/grub/disk.h b/include/grub/disk.h
> index be032a72c..608deb034 100644
> --- a/include/grub/disk.h
> +++ b/include/grub/disk.h
> @@ -184,14 +184,14 @@ typedef struct grub_disk_memberlist 
> *grub_disk_memberlist_t;
>  #define GRUB_MDRAID_MAX_DISKS        4096
>  
>  /* The size of a disk cache in 512B units. Must be at least as big as the
> -   largest supported sector size, currently 16K.  */
> -#define GRUB_DISK_CACHE_BITS 6
> +   largest supported sector size, currently 64K.  */
> +#define GRUB_DISK_CACHE_BITS 7

This change is not reflected in the commit message and is not obvious
why this is changed. Is it necessary due to the change below or
additional performance improvement?

Glenn

>  #define GRUB_DISK_CACHE_SIZE (1 << GRUB_DISK_CACHE_BITS)
>  
>  #define GRUB_DISK_MAX_MAX_AGGLOMERATE ((1 << (30 - GRUB_DISK_CACHE_BITS - 
> GRUB_DISK_SECTOR_BITS)) - 1)
>  
>  /* Maximum number of sectors to read in LBA mode at once */
> -#define GRUB_DISK_MAX_LBA_SECTORS 63
> +#define GRUB_DISK_MAX_LBA_SECTORS 127
>  
>  /* Return value of grub_disk_native_sectors() in case disk size is unknown. 
> */
>  #define GRUB_DISK_SIZE_UNKNOWN        0xffffffffffffffffULL