On Mon, Feb 02, 2026 at 11:04:08AM -0500, Michael S. Tsirkin wrote: > 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.
This command-line lets you benchmark virtio-blk without actual I/O
slowing down the request processing:
qemu-system-x86_64 \
-M accel=kvm \
-cpu host \
-m 4G \
--blockdev
file,node-name=drive0,filename=boot.img,cache.direct=on,aio=native \
--blockdev null-co,node-name=drive1,size=$((10 * 1024 * 1024 * 1024)) \
--object iothread,id=iothread0 \
--device virtio-blk-pci,drive=drive0,iothread=iothread0 \
--device virtio-blk-pci,drive=drive1,iothread=iothread0
Here is a fio command-line for 4 KiB random reads:
fio \
--ioengine=libaio \
--direct=1 \
--runtime=30 \
--ramp_time=10 \
--rw=randread \
--bs=4k \
--iodepth=128 \
--filename=/dev/vdb \
--name=randread
This is just a single vCPU, but it should be enough to see if there is
any difference in I/O Operations Per Second (IOPS) or efficiency
(IOPS/CPU utilization).
>
>
> > >
> > >
> > >
> > >> @@ -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
>
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