Re: [Qemu-devel] [RFC 07/12] Store the data to send also in iovec

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, Mar 21, 2013 at 01:10:40PM +0200, Orit Wasserman wrote:
> On 03/21/2013 11:56 AM, Paolo Bonzini wrote:
> > Il 21/03/2013 10:09, Orit Wasserman ha scritto:
> >> All data is still copied into the static buffer.
> >>
> >> Signed-off-by: Orit Wasserman <owasserm@redhat.com>
> >> ---
> >>  savevm.c | 13 +++++++++++--
> >>  1 file changed, 11 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/savevm.c b/savevm.c
> >> index ec64533..d5834ca 100644
> >> --- a/savevm.c
> >> +++ b/savevm.c
> >> @@ -114,6 +114,7 @@ void qemu_announce_self(void)
> >>  /* savevm/loadvm support */
> >>  
> >>  #define IO_BUF_SIZE 32768
> >> +#define MAX_IOV_SIZE 64
> > 
> > You could use IOV_MAX, or min(IOV_MAX, 64).
> Sure
>  The 64 should be tuned on a
> > good 10G network...
> 
> You need to remember that iovec of 64 is equivalent to 32 guest pages which are 
> 128K data. This is a large TCP packet that will be fragmented even with jumbo frames.
> I can make it configurable but not sure if it will be useful.
> Micheal, what do you think?
> 
> Orit

You are both right :). 64 looks like a sane value, and we can
try and tune it some more if we have the time.

> > 
> > Paolo
> > 
> >>  struct QEMUFile {
> >>      const QEMUFileOps *ops;
> >> @@ -129,6 +130,9 @@ struct QEMUFile {
> >>      int buf_size; /* 0 when writing */
> >>      uint8_t buf[IO_BUF_SIZE];
> >>  
> >> +    struct iovec iov[MAX_IOV_SIZE];
> >> +    unsigned int iovcnt;
> >> +
> >>      int last_error;
> >>  };
> >>  
> >> @@ -546,6 +550,7 @@ static void qemu_fflush(QEMUFile *f)
> >>              f->pos += f->buf_index;
> >>          }
> >>          f->buf_index = 0;
> >> +        f->iovcnt = 0;
> >>      }
> >>      if (ret < 0) {
> >>          qemu_file_set_error(f, ret);
> >> @@ -638,12 +643,14 @@ void qemu_put_buffer(QEMUFile *f, const uint8_t *buf, int size)
> >>          if (l > size)
> >>              l = size;
> >>          memcpy(f->buf + f->buf_index, buf, l);
> >> +        f->iov[f->iovcnt].iov_base = f->buf + f->buf_index;
> >> +        f->iov[f->iovcnt++].iov_len = l;
> >>          f->is_write = 1;
> >>          f->buf_index += l;
> >>          f->bytes_xfer += l;
> >>          buf += l;
> >>          size -= l;
> >> -        if (f->buf_index >= IO_BUF_SIZE) {
> >> +        if (f->buf_index >= IO_BUF_SIZE || f->iovcnt >= MAX_IOV_SIZE) {
> >>              qemu_fflush(f);
> >>              if (qemu_file_get_error(f)) {
> >>                  break;
> >> @@ -667,8 +674,10 @@ void qemu_put_byte(QEMUFile *f, int v)
> >>      f->buf[f->buf_index++] = v;
> >>      f->is_write = 1;
> >>      f->bytes_xfer += 1;
> >> +    f->iov[f->iovcnt].iov_base = f->buf + (f->buf_index - 1);
> >> +    f->iov[f->iovcnt++].iov_len = 1;
> >>  
> >> -    if (f->buf_index >= IO_BUF_SIZE) {
> >> +    if (f->buf_index >= IO_BUF_SIZE || f->iovcnt >= MAX_IOV_SIZE) {
> >>          qemu_fflush(f);
> >>      }
> >>  }
> >>
> >