Re: [PATCH v3 04/11] hw/virtio: Use VirtIODevice::access_is_big_endian field

["Michael S. Tsirkin" <mst@redhat.com>]

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 <philmd@linaro.org>
> ---
>  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.



> @@ -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