[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
[Qemu-devel] [PATCH v2 5/5] virtio: optimize virtio_access_is_big_endian
From: |
Greg Kurz |
Subject: |
[Qemu-devel] [PATCH v2 5/5] virtio: optimize virtio_access_is_big_endian() for little-endian targets |
Date: |
Mon, 11 Jan 2016 17:18:06 +0100 |
User-agent: |
StGit/0.17.1-dirty |
When adding cross-endian support, we introduced the TARGET_IS_BIENDIAN macro
and the virtio_access_is_big_endian() helper to have a branchless fast path
in the virtio memory accessors for targets that don't switch endian.
This was considered as a strong requirement at the time.
Now we have added a runtime check for virtio 1.0, which ruins the benefit
of the virtio_access_is_big_endian() helper for always little-endian targets.
With this patch, always little-endian targets stop checking for virtio 1.0,
since the result is little-endian in all cases.
Signed-off-by: Greg Kurz <address@hidden>
---
v2:
- simplified the logic as suggested by Laurent Vivier
---
include/hw/virtio/virtio-access.h | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/include/hw/virtio/virtio-access.h
b/include/hw/virtio/virtio-access.h
index f1f12afe9089..8dc84f520316 100644
--- a/include/hw/virtio/virtio-access.h
+++ b/include/hw/virtio/virtio-access.h
@@ -19,13 +19,13 @@
static inline bool virtio_access_is_big_endian(VirtIODevice *vdev)
{
+#if defined(TARGET_IS_BIENDIAN)
+ return virtio_is_big_endian(vdev);
+#elif defined(TARGET_WORDS_BIGENDIAN)
if (virtio_vdev_has_feature(vdev, VIRTIO_F_VERSION_1)) {
/* Devices conforming to VIRTIO 1.0 or later are always LE. */
return false;
}
-#if defined(TARGET_IS_BIENDIAN)
- return virtio_is_big_endian(vdev);
-#elif defined(TARGET_WORDS_BIGENDIAN)
return true;
#else
return false;
- Re: [Qemu-devel] [PATCH v2 1/5] virtio-net: use the backend cross-endian capabilities, (continued)
[Qemu-devel] [PATCH v2 2/5] Revert "vhost-net: tell tap backend about the vnet endianness", Greg Kurz, 2016/01/11
[Qemu-devel] [PATCH v2 3/5] virtio: move cross-endian helper to vhost, Greg Kurz, 2016/01/11
[Qemu-devel] [PATCH v2 4/5] vhost: move virtio 1.0 check to cross-endian helper, Greg Kurz, 2016/01/11
[Qemu-devel] [PATCH v2 5/5] virtio: optimize virtio_access_is_big_endian() for little-endian targets,
Greg Kurz <=