Re: [PATCH 12/14] migration/multifd: multifd_send_prepare_header()

[Fabiano Rosas]

peterx@redhat.com writes:

> From: Peter Xu <peterx@redhat.com>
>
> Introduce a helper multifd_send_prepare_header() to setup the header packet
> for multifd sender.
>
> It's fine to setup the IOV[0] _before_ send_prepare() because the packet
> buffer is already ready, even if the content is to be filled in.
>
> With this helper, we can already slightly clean up the zero copy path.
>
> Note that I explicitly put it into multifd.h, because I want it inlined
> directly into multifd*.c where necessary later.
>
> Signed-off-by: Peter Xu <peterx@redhat.com>

Reviewed-by: Fabiano Rosas <farosas@suse.de>

nit below:

> ---
>  migration/multifd.h |  8 ++++++++
>  migration/multifd.c | 16 ++++++++--------
>  2 files changed, 16 insertions(+), 8 deletions(-)
>
> diff --git a/migration/multifd.h b/migration/multifd.h
> index 2e4ad0dc56..4ec005f53f 100644
> --- a/migration/multifd.h
> +++ b/migration/multifd.h
> @@ -209,5 +209,13 @@ typedef struct {
>  
>  void multifd_register_ops(int method, MultiFDMethods *ops);
>  
> +static inline void multifd_send_prepare_header(MultiFDSendParams *p)
> +{
> +    p->iov[0].iov_len = p->packet_len;
> +    p->iov[0].iov_base = p->packet;
> +    p->iovs_num++;
> +}
> +
> +
>  #endif
>  
> diff --git a/migration/multifd.c b/migration/multifd.c
> index 8d4b80f365..1b0035787e 100644
> --- a/migration/multifd.c
> +++ b/migration/multifd.c
> @@ -707,10 +707,14 @@ static void *multifd_send_thread(void *opaque)
>          if (p->pending_job) {
>              MultiFDPages_t *pages = p->pages;
>  
> -            if (use_zero_copy_send) {
> -                p->iovs_num = 0;
> -            } else {
> -                p->iovs_num = 1;
> +            p->iovs_num = 0;
> +
> +            if (!use_zero_copy_send) {
> +                /*
> +                 * Only !zero_copy needs the header in IOV; zerocopy will
> +                 * send it separately.

Could use the same spelling for both mentions to zero copy.

> +                 */
> +                multifd_send_prepare_header(p);
>              }
>  
>              assert(pages->num);
> @@ -730,10 +734,6 @@ static void *multifd_send_thread(void *opaque)
>                  if (ret != 0) {
>                      break;
>                  }
> -            } else {
> -                /* Send header using the same writev call */
> -                p->iov[0].iov_len = p->packet_len;
> -                p->iov[0].iov_base = p->packet;
>              }
>  
>              ret = qio_channel_writev_full_all(p->c, p->iov, p->iovs_num, 
> NULL,