Re: [PATCH] vhost: fix performance on LE hosts

Greg Kurz
2015-10-27T10:30:34Z

On Tue, 27 Oct 2015 11:37:39 +0200
"Michael S. Tsirkin" <mst@redhat.com> wrote:
> commit 2751c9882b947292fcfb084c4f604e01724af804 ("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>

Oops my bad for this oversight...

Reviewed-by: Greg Kurz <gkurz@linux.vnet.ibm.com>

> ---
> drivers/vhost/vhost.h | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
> index 4772862..d3f7674 100644
> --- 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)