Re: [PATCH] vhost: fix performance on LE hosts
From: Greg Kurz <hidden>
Date: 2015-10-27 10:30:34
Also in:
kvm, lkml, virtualization
On Tue, 27 Oct 2015 11:37:39 +0200 "Michael S. Tsirkin" [off-list ref] 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 <redacted>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>Oops my bad for this oversight... Reviewed-by: Greg Kurz <redacted>
quoted hunk ↗ jump to hunk
--- 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)