488f069bd1
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> |
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| .. | ||
| apic_internal.h | ||
| apic-msidef.h | ||
| apic.h | ||
| ich9.h | ||
| ioapic_internal.h | ||
| ioapic.h | ||
| pc.h | ||
| smbios.h | ||