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| author | Michael S. Tsirkin <mst@redhat.com> | 2013-07-11 16:06:46 +0300 |
|---|---|---|
| committer | Michael S. Tsirkin <mst@redhat.com> | 2013-07-15 21:26:26 +0300 |
| commit | 488f069bd1f3aeb6ee748acb02b7581831bcb3f8 (patch) | |
| tree | 2a696b07fe49fe6e76293d4882fa0467e2d29338 /include/hw/i386 | |
| parent | b1be42803b31a913bab65bab563a8760ad2e7f7f (diff) | |
| download | qemu-488f069bd1f3aeb6ee748acb02b7581831bcb3f8.tar.gz | |
virtio-net: add feature bit for any header s/g
Old qemu versions required that 1st s/g entry is the header.
Since QEMU 1.5, patchset titled "virtio-net: iovec handling cleanup"
removed this limitation but a feature bit is needed so guests know it's
safe to lay out header differently.
This patch applies on top and adds such a feature bit to QEMU.
It is set by default for virtio-net.
virtio net header inline with the data is beneficial
for latency and small packet bandwidth - guest driver
code utilizing this feature has been acked but missed 3.11
by a narrow margin, it's pending for 3.12.
This feature bit is cleared by default when compatibility with old
machine types is requested.
Other performance-sensitive devices (blk and scsi)
don't yet support arbitrary s/g layouts, so
we only set this bit for virtio-net for now.
There are plans to allow arbitrary layouts there, but
no code has been posted yet.
Cc: Rusty Russell <rusty@rustcorp.com.au>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Diffstat (limited to 'include/hw/i386')
| -rw-r--r-- | include/hw/i386/pc.h | 4 |
1 files changed, 4 insertions, 0 deletions
diff --git a/include/hw/i386/pc.h b/include/hw/i386/pc.h index 5949e7ec5f..751592a1e7 100644 --- a/include/hw/i386/pc.h +++ b/include/hw/i386/pc.h @@ -229,6 +229,10 @@ int e820_add_entry(uint64_t, uint64_t, uint32_t); .driver = "Nehalem-" TYPE_X86_CPU,\ .property = "level",\ .value = stringify(2),\ + },{\ + .driver = "virtio-net-pci",\ + .property = "any_layout",\ + .value = "off",\ } #define PC_COMPAT_1_4 \ |