Re: [PATCH v2 15/16] migration/rdma: Simplify the function that saves a page

[Leonardo Bras Soares Passos]

On Fri, May 26, 2023 at 5:21 AM Juan Quintela <quintela@redhat.com> wrote:
>
> Leonardo Brás <leobras@redhat.com> wrote:
> > On Mon, 2023-05-15 at 21:57 +0200, Juan Quintela wrote:
> >> When we sent a page through QEMUFile hooks (RDMA) there are three
> >> posiblities:
> >> - We are not using RDMA. return RAM_SAVE_CONTROL_DELAYED and
> >>   control_save_page() returns false to let anything else to proceed.
> >> - There is one error but we are using RDMA.  Then we return a negative
> >>   value, control_save_page() needs to return true.
> >> - Everything goes well and RDMA start the sent of the page
> >>   asynchronously.  It returns RAM_SAVE_CONTROL_DELAYED and we need to
> >>   return 1 for ram_save_page_legacy.
> >>
> >> Clear?
> >>
> >> I know, I know, the interfaz is as bad as it gets.  I think that now
> >> it is a bit clearer, but this needs to be done some other way.
> >
> > interface?
>
> Yeap.  I used the Spanish spelling, that, you know, in English is wrong O:-)

Happens to me all the time :)

>
> Thanks.
> >> diff --git a/migration/rdma.c b/migration/rdma.c
> >> index 416dec00a2..12d3c23fdc 100644
> >> --- a/migration/rdma.c
> >> +++ b/migration/rdma.c
> >> @@ -3239,13 +3239,12 @@ qio_channel_rdma_shutdown(QIOChannel *ioc,
> >>   *
> >>   *    @size : Number of bytes to transfer
> >>   *
> >> - *    @bytes_sent : User-specificed pointer to indicate how many bytes 
> >> were
> >> + *    @pages_sent : User-specificed pointer to indicate how many pages 
> >> were
> >>   *                  sent. Usually, this will not be more than a few bytes 
> >> of
> >>   *                  the protocol because most transfers are sent 
> >> asynchronously.
> >>   */
> >
> > There is new doc to pages_sent but the parameter is not added to the 
> > signature
> > bellow. Am I missing something?
>
> Good catch.

:)

>
> I redid this patch several times.  And it appears that I forgot some 
> leftovers.
>
> >
> >> -static size_t qemu_rdma_save_page(QEMUFile *f,
> >> -                                  ram_addr_t block_offset, ram_addr_t 
> >> offset,
> >> -                                  size_t size, uint64_t *bytes_sent)
> >> +static int qemu_rdma_save_page(QEMUFile *f, ram_addr_t block_offset,
> >> +                               ram_addr_t offset, size_t size)
> >>  {
> >>      QIOChannelRDMA *rioc = QIO_CHANNEL_RDMA(qemu_file_get_ioc(f));
> >>      RDMAContext *rdma;
> >> @@ -3277,18 +3276,6 @@ static size_t qemu_rdma_save_page(QEMUFile *f,
> >>          goto err;
> >>      }
> >>
> >> -    /*
> >> -     * We always return 1 bytes because the RDMA
> >> -     * protocol is completely asynchronous. We do not yet know
> >> -     * whether an  identified chunk is zero or not because we're
> >> -     * waiting for other pages to potentially be merged with
> >> -     * the current chunk. So, we have to call qemu_update_position()
> >> -     * later on when the actual write occurs.
> >> -     */
> >> -    if (bytes_sent) {
> >> -        *bytes_sent = 1;
> >> -    }
> >> -
> >>      /*
> >>       * Drain the Completion Queue if possible, but do not block,
> >>       * just poll.
> >
> > Oh, so this one complements 13/16.
> > Since it doesn't do imaginary transfers anymore, there is no need to use
> > bytes_sent pointer to keep track of them anymore.
> >
> > Other than the pages_sent above that I couldn't understand:
> > Reviewed-by: Leonardo Bras <leobras@redhat.com>
>
> Dropping that bit.
>
> Thanks.
>