[edk2-devel] [PATCH v2 02/10] OvmfPkg: raise PcdShellFileOperationSize to 128KB
Philippe Mathieu-Daudé
philmd at redhat.com
Fri Jan 15 09:34:41 UTC 2021
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 at arm.com>
> Cc: Jordan Justen <jordan.l.justen at intel.com>
> Cc: Philippe Mathieu-Daudé <philmd at redhat.com>
> Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=3125
> Signed-off-by: Laszlo Ersek <lersek at redhat.com>
> Acked-by: Ard Biesheuvel <ard.biesheuvel at 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(+)
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