Re: [PATCH v2 02/10] OvmfPkg: raise PcdShellFileOperationSize to 128KB

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

Hi Laszlo,

On 1/13/21 9:54 AM, Laszlo Ersek wrote:
> Some UEFI shell commands read and write files in chunks. The chunk size is
> given by "PcdShellFileOperationSize", whose default in
> "ShellPkg/ShellPkg.dec" is 4KB (0x1000).
> 
> The virtio-fs daemon of QEMU advertizes a 128KB maximum buffer size by
> default, for the FUSE_WRITE operation.

I delayed this patch review because I couldn't find where this value
is advertized in QEMU (virtiofsd is very new to me). Can you enlighten
me please?

> By raising PcdShellFileOperationSize 32-fold, the number of FUSE write
> requests shrinks proportionately, when writing large files. And when a
> Virtio Filesystem is not used, a 128KB chunk size is still not
> particularly wasteful.
> 
> Some ad-hoc measurements on my laptop, using OVMF:
> 
> - The time it takes to copy a ~270MB file from a Virtio Filesystem to the
>   same Virtio Filesystem improves from ~9 seconds to ~1 second.
> 
> - The time it takes to compare two identical ~270MB files on the same
>   Virtio Filesystem improves from ~11 seconds to ~3 seconds.
> 
> Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>
> Cc: Jordan Justen <jordan.l.justen@intel.com>
> Cc: Philippe Mathieu-Daudé <philmd@redhat.com>
> Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=3125
> Signed-off-by: Laszlo Ersek <lersek@redhat.com>
> Acked-by: Ard Biesheuvel <ard.biesheuvel@arm.com>
> ---
> 
> Notes:
>     v2:
>     - no changes
>     - pick up Ard's A-b
> 
>  OvmfPkg/OvmfPkgIa32.dsc    | 2 ++
>  OvmfPkg/OvmfPkgIa32X64.dsc | 2 ++
>  OvmfPkg/OvmfPkgX64.dsc     | 2 ++
>  3 files changed, 6 insertions(+)