From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:46563) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aImuE-0007y2-SR for qemu-devel@nongnu.org; Mon, 11 Jan 2016 19:33:51 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1aImuD-0007nL-MN for qemu-devel@nongnu.org; Mon, 11 Jan 2016 19:33:50 -0500 Received: from mx1.redhat.com ([209.132.183.28]:44177) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aImuD-0007nH-Gl for qemu-devel@nongnu.org; Mon, 11 Jan 2016 19:33:49 -0500 References: <20160111161156.17428.20668.stgit@bahia.huguette.org> <20160111161317.17428.44013.stgit@bahia.huguette.org> From: Laurent Vivier Message-ID: <569449EB.9070108@redhat.com> Date: Tue, 12 Jan 2016 01:33:47 +0100 MIME-Version: 1.0 In-Reply-To: <20160111161317.17428.44013.stgit@bahia.huguette.org> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH v2 5/5] virtio: optimize virtio_access_is_big_endian() for little-endian targets List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Greg Kurz , "Michael S. Tsirkin" Cc: qemu-devel@nongnu.org On 11/01/2016 17:18, Greg Kurz wrote: > 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 > --- > 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; > > Reviewed-by: Laurent Vivier