Re: [PATCH v3 15/23] multifd: Use a single writev on the send side

[Dr. David Alan Gilbert]

* Juan Quintela (quintela@redhat.com) wrote:
> Until now, we wrote the packet header with write(), and the rest of the
> pages with writev().  Just increase the size of the iovec and do a
> single writev().
> 
> Signed-off-by: Juan Quintela <quintela@redhat.com>

Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

> ---
>  migration/multifd.c | 20 ++++++++------------
>  1 file changed, 8 insertions(+), 12 deletions(-)
> 
> diff --git a/migration/multifd.c b/migration/multifd.c
> index 71bdef068e..65676d56fd 100644
> --- a/migration/multifd.c
> +++ b/migration/multifd.c
> @@ -643,7 +643,7 @@ static void *multifd_send_thread(void *opaque)
>              uint32_t used = p->pages->num;
>              uint64_t packet_num = p->packet_num;
>              uint32_t flags = p->flags;
> -            p->iovs_num = 0;
> +            p->iovs_num = 1;
>  
>              if (used) {
>                  ret = multifd_send_state->ops->send_prepare(p, &local_err);
> @@ -663,20 +663,15 @@ static void *multifd_send_thread(void *opaque)
>              trace_multifd_send(p->id, packet_num, used, flags,
>                                 p->next_packet_size);
>  
> -            ret = qio_channel_write_all(p->c, (void *)p->packet,
> -                                        p->packet_len, &local_err);
> +            p->iov[0].iov_len = p->packet_len;
> +            p->iov[0].iov_base = p->packet;
> +
> +            ret = qio_channel_writev_all(p->c, p->iov, p->iovs_num,
> +                                         &local_err);
>              if (ret != 0) {
>                  break;
>              }
>  
> -            if (used) {
> -                ret = qio_channel_writev_all(p->c, p->iov, p->iovs_num,
> -                                             &local_err);
> -                if (ret != 0) {
> -                    break;
> -                }
> -            }
> -
>              qemu_mutex_lock(&p->mutex);
>              p->pending_job--;
>              qemu_mutex_unlock(&p->mutex);
> @@ -913,7 +908,8 @@ int multifd_save_setup(Error **errp)
>          p->packet->version = cpu_to_be32(MULTIFD_VERSION);
>          p->name = g_strdup_printf("multifdsend_%d", i);
>          p->tls_hostname = g_strdup(s->hostname);
> -        p->iov = g_new0(struct iovec, page_count);
> +        /* We need one extra place for the packet header */
> +        p->iov = g_new0(struct iovec, page_count + 1);
>          socket_send_channel_create(multifd_new_send_channel_async, p);
>      }
>  
> -- 
> 2.33.1
> 
-- 
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK