Re: [Qemu-devel] [PATCH v3 9/9] coalesce adjacent iovecs

[Michael S. Tsirkin]

On Thu, Mar 21, 2013 at 06:27:42PM +0200, Orit Wasserman wrote:
> On 03/21/2013 06:16 PM, Michael S. Tsirkin wrote:
> > On Thu, Mar 21, 2013 at 06:05:40PM +0200, Orit Wasserman wrote:
> >> This way we send one big buffer instead of many small ones
> >>
> >> Signed-off-by: Orit Wasserman <address@hidden>
> > 
> > Why does this happen BTW?
> 
> It happens in the last phase when we send the device state that consists of a 
> lot
> bytes and int field that are written using qemu_put_byte/be16/...
> 

Confused  I thought device_state does not use _nocopy?
My idea of using vmsplice relies exactly on this:
we can not splice device state ...

> > 
> >> ---
> >>  savevm.c | 21 +++++++++++++++++----
> >>  1 file changed, 17 insertions(+), 4 deletions(-)
> >>
> >> diff --git a/savevm.c b/savevm.c
> >> index 50e8fb2..13a533b 100644
> >> --- a/savevm.c
> >> +++ b/savevm.c
> >> @@ -634,8 +634,14 @@ void qemu_put_buffer_no_copy(QEMUFile *f, const 
> >> uint8_t *buf, int size)
> >>          abort();
> >>      }
> >>  
> >> -    f->iov[f->iovcnt].iov_base = (uint8_t *)buf;
> >> -    f->iov[f->iovcnt++].iov_len = size;
> >> +    /* check for adjoint buffer and colace them */
> >> +    if (f->iovcnt > 0 && buf == f->iov[f->iovcnt - 1].iov_base +
> >> +        f->iov[f->iovcnt - 1].iov_len) {
> >> +        f->iov[f->iovcnt - 1].iov_len += size;
> >> +    } else {
> >> +        f->iov[f->iovcnt].iov_base = (uint8_t *)buf;
> >> +        f->iov[f->iovcnt++].iov_len = size;
> >> +    }
> >>  
> >>      f->is_write = 1;
> >>      f->bytes_xfer += size;
> >> @@ -690,8 +696,15 @@ 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;
> >> +
> >> +    /* check for adjoint buffer and colace them */
> >> +    if (f->iovcnt > 0 && f->buf + (f->buf_index - 1)  ==
> >> +        f->iov[f->iovcnt - 1].iov_base + f->iov[f->iovcnt - 1].iov_len) {
> >> +        f->iov[f->iovcnt - 1].iov_len += 1;
> >> +    } else {
> >> +        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 || f->iovcnt >= MAX_IOV_SIZE) {
> >>          qemu_fflush(f);
> >> -- 
> >> 1.7.11.7