Re: [RFC PATCH-for-8.0 07/10] hw/virtio: Directly access cached VirtIODevice::access_is_big_endian

[Greg Kurz]

On Tue, 13 Dec 2022 00:05:14 +0100
Philippe Mathieu-Daudé <philmd@linaro.org> wrote:

> Since the device endianness doesn't change at runtime,
> use the cached value instead of evaluating it on each call.
> 
> Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
> ---
>  include/hw/virtio/virtio-access.h | 44 +++++++++++++++----------------
>  1 file changed, 22 insertions(+), 22 deletions(-)
> 
> diff --git a/include/hw/virtio/virtio-access.h 
> b/include/hw/virtio/virtio-access.h
> index 07aae69042..985f39fe16 100644
> --- a/include/hw/virtio/virtio-access.h
> +++ b/include/hw/virtio/virtio-access.h
> @@ -43,7 +43,7 @@ static inline uint16_t virtio_lduw_phys(VirtIODevice *vdev, 
> hwaddr pa)
>  {
>      AddressSpace *dma_as = vdev->dma_as;
>  
> -    if (virtio_access_is_big_endian(vdev)) {
> +    if (vdev->access_is_big_endian) {

For x86, virtio_access_is_big_endian() expands to :

static inline bool virtio_access_is_big_endian(VirtIODevice *vdev)
{
    return false;
}

When I added these memory accessors, there was a strong requirement from MST
that x86 shouldn't have to pay for an out-of-line check when it is known that
everything is always little endian. Not sure exactly what you're trying to
achieve with VirtIODevice::access_is_big_endian but this shouldn't mess with
this fast path.

>          return lduw_be_phys(dma_as, pa);
>      }
>      return lduw_le_phys(dma_as, pa);
> @@ -53,7 +53,7 @@ static inline uint32_t virtio_ldl_phys(VirtIODevice *vdev, 
> hwaddr pa)
>  {
>      AddressSpace *dma_as = vdev->dma_as;
>  
> -    if (virtio_access_is_big_endian(vdev)) {
> +    if (vdev->access_is_big_endian) {
>          return ldl_be_phys(dma_as, pa);
>      }
>      return ldl_le_phys(dma_as, pa);
> @@ -63,7 +63,7 @@ static inline uint64_t virtio_ldq_phys(VirtIODevice *vdev, 
> hwaddr pa)
>  {
>      AddressSpace *dma_as = vdev->dma_as;
>  
> -    if (virtio_access_is_big_endian(vdev)) {
> +    if (vdev->access_is_big_endian) {
>          return ldq_be_phys(dma_as, pa);
>      }
>      return ldq_le_phys(dma_as, pa);
> @@ -74,7 +74,7 @@ static inline void virtio_stw_phys(VirtIODevice *vdev, 
> hwaddr pa,
>  {
>      AddressSpace *dma_as = vdev->dma_as;
>  
> -    if (virtio_access_is_big_endian(vdev)) {
> +    if (vdev->access_is_big_endian) {
>          stw_be_phys(dma_as, pa, value);
>      } else {
>          stw_le_phys(dma_as, pa, value);
> @@ -86,7 +86,7 @@ static inline void virtio_stl_phys(VirtIODevice *vdev, 
> hwaddr pa,
>  {
>      AddressSpace *dma_as = vdev->dma_as;
>  
> -    if (virtio_access_is_big_endian(vdev)) {
> +    if (vdev->access_is_big_endian) {
>          stl_be_phys(dma_as, pa, value);
>      } else {
>          stl_le_phys(dma_as, pa, value);
> @@ -95,7 +95,7 @@ static inline void virtio_stl_phys(VirtIODevice *vdev, 
> hwaddr pa,
>  
>  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);
> @@ -104,7 +104,7 @@ 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);
> @@ -113,7 +113,7 @@ 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);
> @@ -122,7 +122,7 @@ 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);
> @@ -131,7 +131,7 @@ 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);
> @@ -140,7 +140,7 @@ 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);
> @@ -150,9 +150,9 @@ 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
>  }
>  
> @@ -160,7 +160,7 @@ 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);
> @@ -170,7 +170,7 @@ static inline uint32_t 
> virtio_ldl_phys_cached(VirtIODevice *vdev,
>                                                MemoryRegionCache *cache,
>                                                hwaddr pa)
>  {
> -    if (virtio_access_is_big_endian(vdev)) {
> +    if (vdev->access_is_big_endian) {
>          return ldl_be_phys_cached(cache, pa);
>      }
>      return ldl_le_phys_cached(cache, pa);
> @@ -180,7 +180,7 @@ static inline uint64_t 
> virtio_ldq_phys_cached(VirtIODevice *vdev,
>                                                MemoryRegionCache *cache,
>                                                hwaddr pa)
>  {
> -    if (virtio_access_is_big_endian(vdev)) {
> +    if (vdev->access_is_big_endian) {
>          return ldq_be_phys_cached(cache, pa);
>      }
>      return ldq_le_phys_cached(cache, pa);
> @@ -190,7 +190,7 @@ 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);
> @@ -201,7 +201,7 @@ static inline void virtio_stl_phys_cached(VirtIODevice 
> *vdev,
>                                            MemoryRegionCache *cache,
>                                            hwaddr pa, uint32_t value)
>  {
> -    if (virtio_access_is_big_endian(vdev)) {
> +    if (vdev->access_is_big_endian) {
>          stl_be_phys_cached(cache, pa, value);
>      } else {
>          stl_le_phys_cached(cache, pa, value);
> @@ -216,9 +216,9 @@ 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
>  }
>  
> @@ -230,9 +230,9 @@ 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
>  }
>