vhost: fix performance on LE hosts

mstsirkin · davem330 · commit e407f39afdc0 · 2015-10-27T20:17:03.000-07:00
commit 2751c98 ("vhost: cross-endian support for legacy devices") introduced a minor regression: even with cross-endian disabled, and even on LE host, vhost_is_little_endian is checking is_le flag so there's always a branch. To fix, simply check virtio_legacy_is_little_endian first. Cc: Greg Kurz <gkurz@linux.vnet.ibm.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com> Reviewed-by: Greg Kurz <gkurz@linux.vnet.ibm.com> Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
@@ -183,10 +183,17 @@ static inline bool vhost_has_feature(struct vhost_virtqueue *vq, int bit)
 	return vq->acked_features & (1ULL << bit);
 }
 
+#ifdef CONFIG_VHOST_CROSS_ENDIAN_LEGACY
 static inline bool vhost_is_little_endian(struct vhost_virtqueue *vq)
 {
 	return vq->is_le;
 }
+#else
+static inline bool vhost_is_little_endian(struct vhost_virtqueue *vq)
+{
+	return virtio_legacy_is_little_endian() || vq->is_le;
+}
+#endif
 
 /* Memory accessors */
 static inline u16 vhost16_to_cpu(struct vhost_virtqueue *vq, __virtio16 val)

Original file line number	Diff line number	Diff line change
`@@ -183,10 +183,17 @@ static inline bool vhost_has_feature(struct vhost_virtqueue *vq, int bit)`
`183`	`183`	`return vq->acked_features & (1ULL << bit);`
`184`	`184`	`}`
`185`	`185`
	`186`	`+#ifdef CONFIG_VHOST_CROSS_ENDIAN_LEGACY`
`186`	`187`	`static inline bool vhost_is_little_endian(struct vhost_virtqueue *vq)`
`187`	`188`	`{`
`188`	`189`	`return vq->is_le;`
`189`	`190`	`}`
	`191`	`+#else`
	`192`	`+static inline bool vhost_is_little_endian(struct vhost_virtqueue *vq)`
	`193`	`+{`
	`194`	`+ return virtio_legacy_is_little_endian() \|\| vq->is_le;`
	`195`	`+}`
	`196`	`+#endif`
`190`	`197`
`191`	`198`	`/* Memory accessors */`
`192`	`199`	`static inline u16 vhost16_to_cpu(struct vhost_virtqueue *vq, __virtio16 val)`