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

Subject: Re: Grub2 EFI: Image loading from USB takes too long
Date: Tue, 5 Apr 2011 12:47:30 +0530

On Tue, Apr 5, 2011 at 12:02, Seth Goldberg <address@hidden> wrote:
> It's not just USB.  Loading large files via UEFI with GRUB2 takes an 
> extremely long time.  One of the things phcoder suggested was changing the 
> cache size, which you've done.  Od love to see a larger cache committed to 
> the trunk so UEFI platforms can benefit when large files need to be read by 
> GRUB2 (assuming no other side effects)!
>  --S
> On Apr 4, 2011, at 10:33 PM, Aravind Srinivasan <address@hidden> wrote:
>> Hi,
>> I am trying Grub2 EFI - this is on a custom platform. On 1.99-rc1, compared 
>> to
>> Legacy grub, loading image, in particular initrd image from a USB takes a 
>> very
>> long.  Our initrd image is about 160M and it is taking about 2 mins to load 
>> this
>> image. Turning on "set debug=all" in the grub.cfg file, I see that all the 
>> time
>> is being spent in reading the USB. Looking at the source, I think the issue 
>> is
>> the value set for GRUB_DISK_CACHE_SIZE in include/grub/disk.h
>> Currently this is what it is set to:
>> 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.
>> Thanks,
>> -Aravind
>> Insert mode
>> _______________________________________________
>> Grub-devel mailing list
>> address@hidden
> _______________________________________________
> Grub-devel mailing list
> address@hidden

I can confirm that grub2 x86_64-efi is very slow in loading initramfs
files. I did my testing in VirtualBox 4.0.4 (VBox patched OVMF, quite
old compared to updated OVMF) using an iso mounted in a virtual SATA
AHCI CD drive and 1 GiB RAM alloted to the virtual machine. Intel VT
extension was enabled. In a crude benchmarking using s top watch, the
time between selection of menuentry to seeing the kernel boot messages
is approx 4 minutes (236 seconds) measured using a stop watch. I have
not yet tested with an updated ovmf in qemu or in duet. I guess
accessing from HDDs is faster in UEFI systems. Its the CDs and USB
which seem to take a lot of time.

The kernel loaded by grub2 during the test and the initramfs can be
downloaded from  - kernel (lzma
compressed)  -
initramfs (lzma -9 compressed cpio archive).



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