Re: [Qemu-devel] [PATCH 07/10] virtio: combine the read of a descriptor

[Gonglei (Arei)]

Hi,

> Subject: [Qemu-devel] [PATCH 07/10] virtio: combine the read of a descriptor
> 
> Compared to vring, virtio has a performance penalty of 10%.  Fix it
> by combining all the reads for a descriptor in a single address_space_read
> call.  This also simplifies the code nicely.
> 
> Reviewed-by: Cornelia Huck <address@hidden>
> Signed-off-by: Paolo Bonzini <address@hidden>
> ---
>  hw/virtio/virtio.c | 86 
> ++++++++++++++++++++++--------------------------------
>  1 file changed, 35 insertions(+), 51 deletions(-)
> 

Unbelievable! After applying this patch, the virtio-crypto speed can attach 
74MB/sec, host
Cpu overhead is 180% (the main thread 100% and vcpu threads 80%)

Testing AES-128-CBC cipher: 
        Encrypting in chunks of 256 bytes: done. 371.94 MiB in 5.02 secs: 74.12 
MiB/sec (1523475 packets)
        Encrypting in chunks of 256 bytes: done. 369.85 MiB in 5.01 secs: 73.88 
MiB/sec (1514900 packets)
        Encrypting in chunks of 256 bytes: done. 371.07 MiB in 5.02 secs: 73.97 
MiB/sec (1519914 packets)
        Encrypting in chunks of 256 bytes: done. 371.66 MiB in 5.02 secs: 74.09 
MiB/sec (1522309 packets)
        Encrypting in chunks of 256 bytes: done. 371.79 MiB in 5.02 secs: 74.12 
MiB/sec (1522868 packets)
        Encrypting in chunks of 256 bytes: done. 371.94 MiB in 5.02 secs: 74.15 
MiB/sec (1523457 packets)
        Encrypting in chunks of 256 bytes: done. 371.90 MiB in 5.02 secs: 74.14 
MiB/sec (1523317 packets)
        Encrypting in chunks of 256 bytes: done. 371.71 MiB in 5.02 secs: 74.10 
MiB/sec (1522522 packets)

15.95%  qemu-kvm                 [.] address_space_translate
  6.98%  qemu-kvm                 [.] qemu_get_ram_ptr
  4.87%  libpthread-2.19.so       [.] __pthread_mutex_unlock_usercnt
  4.40%  qemu-kvm                 [.] qemu_ram_addr_from_host
  3.79%  qemu-kvm                 [.] address_space_map
  3.41%  libc-2.19.so             [.] _int_malloc
  3.29%  libc-2.19.so             [.] _int_free
  3.07%  libc-2.19.so             [.] malloc
  2.95%  libpthread-2.19.so       [.] pthread_mutex_lock
  2.94%  qemu-kvm                 [.] phys_page_find
  2.73%  qemu-kvm                 [.] address_space_translate_internal
  2.65%  libc-2.19.so             [.] malloc_consolidate
  2.35%  libc-2.19.so             [.] __memcpy_sse2_unaligned
  1.72%  qemu-kvm                 [.] find_next_zero_bit
  1.38%  qemu-kvm                 [.] address_space_rw
  1.34%  qemu-kvm                 [.] object_unref
  1.30%  qemu-kvm                 [.] object_ref
  1.28%  qemu-kvm                 [.] virtqueue_pop
  1.20%  libc-2.19.so             [.] memset
  1.11%  qemu-kvm                 [.] virtio_notify

Thank you so much!

Regards,
-Gonglei

> diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> index 79a635f..2433866 100644
> --- a/hw/virtio/virtio.c
> +++ b/hw/virtio/virtio.c
> @@ -107,35 +107,15 @@ void virtio_queue_update_rings(VirtIODevice *vdev,
> int n)
>                                vring->align);
>  }
> 
> -static inline uint64_t vring_desc_addr(VirtIODevice *vdev, hwaddr desc_pa,
> -                                       int i)
> +static void vring_desc_read(VirtIODevice *vdev, VRingDesc *desc,
> +                            hwaddr desc_pa, int i)
>  {
> -    hwaddr pa;
> -    pa = desc_pa + sizeof(VRingDesc) * i + offsetof(VRingDesc, addr);
> -    return virtio_ldq_phys(vdev, pa);
> -}
> -
> -static inline uint32_t vring_desc_len(VirtIODevice *vdev, hwaddr desc_pa, int
> i)
> -{
> -    hwaddr pa;
> -    pa = desc_pa + sizeof(VRingDesc) * i + offsetof(VRingDesc, len);
> -    return virtio_ldl_phys(vdev, pa);
> -}
> -
> -static inline uint16_t vring_desc_flags(VirtIODevice *vdev, hwaddr desc_pa,
> -                                        int i)
> -{
> -    hwaddr pa;
> -    pa = desc_pa + sizeof(VRingDesc) * i + offsetof(VRingDesc, flags);
> -    return virtio_lduw_phys(vdev, pa);
> -}
> -
> -static inline uint16_t vring_desc_next(VirtIODevice *vdev, hwaddr desc_pa,
> -                                       int i)
> -{
> -    hwaddr pa;
> -    pa = desc_pa + sizeof(VRingDesc) * i + offsetof(VRingDesc, next);
> -    return virtio_lduw_phys(vdev, pa);
> +    address_space_read(&address_space_memory, desc_pa + i *
> sizeof(VRingDesc),
> +                       MEMTXATTRS_UNSPECIFIED, (void *)desc,
> sizeof(VRingDesc));
> +    virtio_tswap64s(vdev, &desc->addr);
> +    virtio_tswap32s(vdev, &desc->len);
> +    virtio_tswap16s(vdev, &desc->flags);
> +    virtio_tswap16s(vdev, &desc->next);
>  }
> 
>  static inline uint16_t vring_avail_flags(VirtQueue *vq)
> @@ -345,18 +325,18 @@ static unsigned int virtqueue_get_head(VirtQueue
> *vq, unsigned int idx)
>      return head;
>  }
> 
> -static unsigned virtqueue_next_desc(VirtIODevice *vdev, hwaddr desc_pa,
> -                                    unsigned int i, unsigned int max)
> +static unsigned virtqueue_read_next_desc(VirtIODevice *vdev, VRingDesc
> *desc,
> +                                         hwaddr desc_pa, unsigned
> int max)
>  {
>      unsigned int next;
> 
>      /* If this descriptor says it doesn't chain, we're done. */
> -    if (!(vring_desc_flags(vdev, desc_pa, i) & VRING_DESC_F_NEXT)) {
> +    if (!(desc->flags & VRING_DESC_F_NEXT)) {
>          return max;
>      }
> 
>      /* Check they're not leading us off end of descriptors. */
> -    next = vring_desc_next(vdev, desc_pa, i);
> +    next = desc->next;
>      /* Make sure compiler knows to grab that: we don't want it changing! */
>      smp_wmb();
> 
> @@ -365,6 +345,7 @@ static unsigned virtqueue_next_desc(VirtIODevice
> *vdev, hwaddr desc_pa,
>          exit(1);
>      }
> 
> +    vring_desc_read(vdev, desc, desc_pa, next);
>      return next;
>  }
> 
> @@ -381,6 +362,7 @@ void virtqueue_get_avail_bytes(VirtQueue *vq,
> unsigned int *in_bytes,
>      while (virtqueue_num_heads(vq, idx)) {
>          VirtIODevice *vdev = vq->vdev;
>          unsigned int max, num_bufs, indirect = 0;
> +        VRingDesc desc;
>          hwaddr desc_pa;
>          int i;
> 
> @@ -388,9 +370,10 @@ void virtqueue_get_avail_bytes(VirtQueue *vq,
> unsigned int *in_bytes,
>          num_bufs = total_bufs;
>          i = virtqueue_get_head(vq, idx++);
>          desc_pa = vq->vring.desc;
> +        vring_desc_read(vdev, &desc, desc_pa, i);
> 
> -        if (vring_desc_flags(vdev, desc_pa, i) & VRING_DESC_F_INDIRECT) {
> -            if (vring_desc_len(vdev, desc_pa, i) % sizeof(VRingDesc)) {
> +        if (desc.flags & VRING_DESC_F_INDIRECT) {
> +            if (desc.len % sizeof(VRingDesc)) {
>                  error_report("Invalid size for indirect buffer table");
>                  exit(1);
>              }
> @@ -403,9 +386,10 @@ void virtqueue_get_avail_bytes(VirtQueue *vq,
> unsigned int *in_bytes,
> 
>              /* loop over the indirect descriptor table */
>              indirect = 1;
> -            max = vring_desc_len(vdev, desc_pa, i) / sizeof(VRingDesc);
> -            desc_pa = vring_desc_addr(vdev, desc_pa, i);
> +            max = desc.len / sizeof(VRingDesc);
> +            desc_pa = desc.addr;
>              num_bufs = i = 0;
> +            vring_desc_read(vdev, &desc, desc_pa, i);
>          }
> 
>          do {
> @@ -415,15 +399,15 @@ void virtqueue_get_avail_bytes(VirtQueue *vq,
> unsigned int *in_bytes,
>                  exit(1);
>              }
> 
> -            if (vring_desc_flags(vdev, desc_pa, i) & VRING_DESC_F_WRITE)
> {
> -                in_total += vring_desc_len(vdev, desc_pa, i);
> +            if (desc.flags & VRING_DESC_F_WRITE) {
> +                in_total += desc.len;
>              } else {
> -                out_total += vring_desc_len(vdev, desc_pa, i);
> +                out_total += desc.len;
>              }
>              if (in_total >= max_in_bytes && out_total >= max_out_bytes) {
>                  goto done;
>              }
> -        } while ((i = virtqueue_next_desc(vdev, desc_pa, i, max)) != max);
> +        } while ((i = virtqueue_read_next_desc(vdev, &desc, desc_pa,
> max)) != max);
> 
>          if (!indirect)
>              total_bufs = num_bufs;
> @@ -545,6 +529,7 @@ void *virtqueue_pop(VirtQueue *vq, size_t sz)
>      unsigned out_num, in_num;
>      hwaddr addr[VIRTQUEUE_MAX_SIZE];
>      struct iovec iov[VIRTQUEUE_MAX_SIZE];
> +    VRingDesc desc;
> 
>      if (!virtqueue_num_heads(vq, vq->last_avail_idx)) {
>          return NULL;
> @@ -560,33 +545,32 @@ void *virtqueue_pop(VirtQueue *vq, size_t sz)
>          vring_set_avail_event(vq, vq->last_avail_idx);
>      }
> 
> -    if (vring_desc_flags(vdev, desc_pa, i) & VRING_DESC_F_INDIRECT) {
> -        if (vring_desc_len(vdev, desc_pa, i) % sizeof(VRingDesc)) {
> +    vring_desc_read(vdev, &desc, desc_pa, i);
> +    if (desc.flags & VRING_DESC_F_INDIRECT) {
> +        if (desc.len % sizeof(VRingDesc)) {
>              error_report("Invalid size for indirect buffer table");
>              exit(1);
>          }
> 
>          /* loop over the indirect descriptor table */
> -        max = vring_desc_len(vdev, desc_pa, i) / sizeof(VRingDesc);
> -        desc_pa = vring_desc_addr(vdev, desc_pa, i);
> +        max = desc.len / sizeof(VRingDesc);
> +        desc_pa = desc.addr;
>          i = 0;
> +        vring_desc_read(vdev, &desc, desc_pa, i);
>      }
> 
>      /* Collect all the descriptors */
>      do {
> -        hwaddr pa = vring_desc_addr(vdev, desc_pa, i);
> -        size_t len = vring_desc_len(vdev, desc_pa, i);
> -
> -        if (vring_desc_flags(vdev, desc_pa, i) & VRING_DESC_F_WRITE) {
> +        if (desc.flags & VRING_DESC_F_WRITE) {
>              virtqueue_map_desc(&in_num, addr + out_num, iov +
> out_num,
> -                               VIRTQUEUE_MAX_SIZE - out_num, true,
> pa, len);
> +                               VIRTQUEUE_MAX_SIZE - out_num, true,
> desc.addr, desc.len);
>          } else {
>              if (in_num) {
>                  error_report("Incorrect order for descriptors");
>                  exit(1);
>              }
>              virtqueue_map_desc(&out_num, addr, iov,
> -                               VIRTQUEUE_MAX_SIZE, false, pa, len);
> +                               VIRTQUEUE_MAX_SIZE, false,
> desc.addr, desc.len);
>          }
> 
>          /* If we've got too many, that implies a descriptor loop. */
> @@ -594,7 +578,7 @@ void *virtqueue_pop(VirtQueue *vq, size_t sz)
>              error_report("Looped descriptor");
>              exit(1);
>          }
> -    } while ((i = virtqueue_next_desc(vdev, desc_pa, i, max)) != max);
> +    } while ((i = virtqueue_read_next_desc(vdev, &desc, desc_pa, max)) !=
> max);
> 
>      /* Now copy what we have collected and mapped */
>      elem = virtqueue_alloc_element(sz, out_num, in_num);
> --
> 2.5.0
> 
>