On 05/03/2016 21:39, Nikos Filippakis wrote:
> Hello everyone! I am interested in getting to know the codebase a little
> better
> so that I can eventually apply for a GSOC position.
> This is my first attempt at posting a patch to a mailing list, any feedback
> is greatly appreciated.
>
> Signed-off-by: Nikos Filippakis <aesm...@gmail.com>
> ---
> net/net.c | 17 ++++++++++++-----
> 1 file changed, 12 insertions(+), 5 deletions(-)
>
> diff --git a/net/net.c b/net/net.c
> index aebf753..79e9d7c 100644
> --- a/net/net.c
> +++ b/net/net.c
> @@ -710,23 +710,30 @@ ssize_t qemu_send_packet_raw(NetClientState *nc, const
> uint8_t *buf, int size)
> static ssize_t nc_sendv_compat(NetClientState *nc, const struct iovec *iov,
> int iovcnt, unsigned flags)
> {
> - uint8_t buf[NET_BUFSIZE];
> uint8_t *buffer;
> size_t offset;
> + ssize_t ret;
>
> if (iovcnt == 1) {
> buffer = iov[0].iov_base;
> offset = iov[0].iov_len;
> } else {
> - buffer = buf;
> - offset = iov_to_buf(iov, iovcnt, 0, buf, sizeof(buf));
> + buffer = g_malloc(NET_BUFSIZE * sizeof(uint8_t));
> + offset = iov_to_buf(iov, iovcnt, 0, buffer,
> + NET_BUFSIZE * sizeof(uint8_t));
> }
Hi Nikos,
I suspect an allocation (especially a large one) on this path can have a
performance impact. On one hand, nc_sendv_compat is not used in
high-performance network cards (e1000 and virtio-net, for example) so
this is not a major issue. On the other hand, this is the first such
conversion so you could set a good example.
Another possibility thus is to make the buffer smaller (e.g. 2K) and
check the size with iov_size. If the size is at most 2K, you use the
on-stack buffer. If the size is bigger than 2K and smaller than
NET_BUFSIZE, you go through the allocation but you only need to allocate
the correct number of bytes. Finally, if the size is bigger than
NET_BUFSIZE you set errno = EINVAL and return -1.
Thanks,
Paolo
> if (flags & QEMU_NET_PACKET_FLAG_RAW && nc->info->receive_raw) {
> - return nc->info->receive_raw(nc, buffer, offset);
> + ret = nc->info->receive_raw(nc, buffer, offset);
> } else {
> - return nc->info->receive(nc, buffer, offset);
> + ret = nc->info->receive(nc, buffer, offset);
> }
> +
> + if (iovcnt != 1) {
> + g_free(buffer);
> + }
> +
> + return ret;
> }
>
> ssize_t qemu_deliver_packet_iov(NetClientState *sender,
>
