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

[Michael S. Tsirkin]

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?

> ---
>  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