On Mon, Feb 02, 2026 at 01:08:25PM +0000, Alex Bennée wrote:
> "Michael S. Tsirkin" <[email protected]> writes:
>
> > On Mon, Feb 02, 2026 at 12:29:16AM +0100, Philippe Mathieu-Daudé wrote:
> >> Endianness access is constant between device resets.
> >> Use the field instead of calling the same function.
> >
> > yes but the function was inlined and often a NOP. worth mentioning.
> >
> >>
> >> Signed-off-by: Philippe Mathieu-Daudé <[email protected]>
> >> ---
> >> include/hw/virtio/virtio-access.h | 24 ++++++++++++------------
> >> hw/virtio/virtio.c | 4 ++--
> >> 2 files changed, 14 insertions(+), 14 deletions(-)
> >>
> >> diff --git a/include/hw/virtio/virtio-access.h
> >> b/include/hw/virtio/virtio-access.h
> >> index cd17d0c87eb..f3b4d0075b5 100644
> >> --- a/include/hw/virtio/virtio-access.h
> >> +++ b/include/hw/virtio/virtio-access.h
> >> @@ -42,7 +42,7 @@ static inline bool
> >> virtio_access_is_big_endian(VirtIODevice *vdev)
> >>
> >> static inline void virtio_stw_p(VirtIODevice *vdev, void *ptr, uint16_t v)
> >> {
> >> - if (virtio_access_is_big_endian(vdev)) {
> >> + if (vdev->access_is_big_endian) {
> >> stw_be_p(ptr, v);
> >> } else {
> >> stw_le_p(ptr, v);
> >
> >
> > So this is the main extra cost: on an LE host, we now have this branch on
> > every
> > access where previously it was all optimized out.
> >
> > Is it measureable? It is worth testing.
>
> I suspect not given this is a well predicted branch on the control
> plane.
Actually you are right. I meant the cached variants below. Not this one.
> But we can certainly try an measure it. Do we have any virtio
> performance benchmarks?
>
> We only have a few in meson:
>
> ./pyvenv/bin/meson test --benchmark --list
> bufferiszero-bench
> benchmark-crypto-hash
> benchmark-crypto-hmac
> benchmark-crypto-cipher
> benchmark-crypto-akcipher
I usually use fio but whatever blk maintainers use is fine by me.
> >
> >
> >
> >> @@ -51,7 +51,7 @@ static inline void virtio_stw_p(VirtIODevice *vdev, void
> >> *ptr, uint16_t v)
> >>
> >> static inline void virtio_stl_p(VirtIODevice *vdev, void *ptr, uint32_t v)
> >> {
> >> - if (virtio_access_is_big_endian(vdev)) {
> >> + if (vdev->access_is_big_endian) {
> >> stl_be_p(ptr, v);
> >> } else {
> >> stl_le_p(ptr, v);
> >> @@ -60,7 +60,7 @@ static inline void virtio_stl_p(VirtIODevice *vdev, void
> >> *ptr, uint32_t v)
> >>
> >> static inline void virtio_stq_p(VirtIODevice *vdev, void *ptr, uint64_t v)
> >> {
> >> - if (virtio_access_is_big_endian(vdev)) {
> >> + if (vdev->access_is_big_endian) {
> >> stq_be_p(ptr, v);
> >> } else {
> >> stq_le_p(ptr, v);
> >> @@ -69,7 +69,7 @@ static inline void virtio_stq_p(VirtIODevice *vdev, void
> >> *ptr, uint64_t v)
> >>
> >> static inline int virtio_lduw_p(VirtIODevice *vdev, const void *ptr)
> >> {
> >> - if (virtio_access_is_big_endian(vdev)) {
> >> + if (vdev->access_is_big_endian) {
> >> return lduw_be_p(ptr);
> >> } else {
> >> return lduw_le_p(ptr);
> >
> > and this one.
> >
> >
> >> @@ -78,7 +78,7 @@ static inline int virtio_lduw_p(VirtIODevice *vdev,
> >> const void *ptr)
> >>
> >> static inline int virtio_ldl_p(VirtIODevice *vdev, const void *ptr)
> >> {
> >> - if (virtio_access_is_big_endian(vdev)) {
> >> + if (vdev->access_is_big_endian) {
> >> return ldl_be_p(ptr);
> >> } else {
> >> return ldl_le_p(ptr);
> >> @@ -87,7 +87,7 @@ static inline int virtio_ldl_p(VirtIODevice *vdev, const
> >> void *ptr)
> >>
> >> static inline uint64_t virtio_ldq_p(VirtIODevice *vdev, const void *ptr)
> >> {
> >> - if (virtio_access_is_big_endian(vdev)) {
> >> + if (vdev->access_is_big_endian) {
> >> return ldq_be_p(ptr);
> >> } else {
> >> return ldq_le_p(ptr);
> >> @@ -97,9 +97,9 @@ static inline uint64_t virtio_ldq_p(VirtIODevice *vdev,
> >> const void *ptr)
> >> static inline uint16_t virtio_tswap16(VirtIODevice *vdev, uint16_t s)
> >> {
> >> #if HOST_BIG_ENDIAN
> >> - return virtio_access_is_big_endian(vdev) ? s : bswap16(s);
> >> + return vdev->access_is_big_endian ? s : bswap16(s);
> >> #else
> >> - return virtio_access_is_big_endian(vdev) ? bswap16(s) : s;
> >> + return vdev->access_is_big_endian ? bswap16(s) : s;
> >> #endif
> >> }
> >>
> >> @@ -111,9 +111,9 @@ static inline void virtio_tswap16s(VirtIODevice *vdev,
> >> uint16_t *s)
> >> static inline uint32_t virtio_tswap32(VirtIODevice *vdev, uint32_t s)
> >> {
> >> #if HOST_BIG_ENDIAN
> >> - return virtio_access_is_big_endian(vdev) ? s : bswap32(s);
> >> + return vdev->access_is_big_endian ? s : bswap32(s);
> >> #else
> >> - return virtio_access_is_big_endian(vdev) ? bswap32(s) : s;
> >> + return vdev->access_is_big_endian ? bswap32(s) : s;
> >> #endif
> >> }
> >>
> >> @@ -125,9 +125,9 @@ static inline void virtio_tswap32s(VirtIODevice *vdev,
> >> uint32_t *s)
> >> static inline uint64_t virtio_tswap64(VirtIODevice *vdev, uint64_t s)
> >> {
> >> #if HOST_BIG_ENDIAN
> >> - return virtio_access_is_big_endian(vdev) ? s : bswap64(s);
> >> + return vdev->access_is_big_endian ? s : bswap64(s);
> >> #else
> >> - return virtio_access_is_big_endian(vdev) ? bswap64(s) : s;
> >> + return vdev->access_is_big_endian ? bswap64(s) : s;
> >> #endif
> >> }
> >>
> >> diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> >> index 242c207a591..1dc60d37cb4 100644
> >> --- a/hw/virtio/virtio.c
> >> +++ b/hw/virtio/virtio.c
> >> @@ -220,7 +220,7 @@ static inline uint16_t
> >> virtio_lduw_phys_cached(VirtIODevice *vdev,
> >> MemoryRegionCache *cache,
> >> hwaddr pa)
> >> {
> >> - if (virtio_access_is_big_endian(vdev)) {
> >> + if (vdev->access_is_big_endian) {
> >> return lduw_be_phys_cached(cache, pa);
> >> }
> >> return lduw_le_phys_cached(cache, pa);
> >> @@ -230,7 +230,7 @@ static inline void virtio_stw_phys_cached(VirtIODevice
> >> *vdev,
> >> MemoryRegionCache *cache,
> >> hwaddr pa, uint16_t value)
> >> {
> >> - if (virtio_access_is_big_endian(vdev)) {
> >> + if (vdev->access_is_big_endian) {
> >> stw_be_phys_cached(cache, pa, value);
> >> } else {
> >> stw_le_phys_cached(cache, pa, value);
> >> --
> >> 2.52.0
I meant these ones.
> --
> Alex Bennée
> Virtualisation Tech Lead @ Linaro
