netdev - Re: [PATCH RFC net-next] virtio_net: refill buffer right after being used

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Fri, 29 Jul 2011 16:58:04 -0700
From:	Mike Waychison <mikew@...gle.com>
To:	Shirley Ma <mashirle@...ibm.com>
Cc:	Rusty Russell <rusty@...tcorp.com.au>, mst@...hat.com,
	kvm@...r.kernel.org, virtualization@...ts.osdl.org,
	netdev@...r.kernel.org
Subject: Re: [PATCH RFC net-next] virtio_net: refill buffer right after being used

On Fri, Jul 29, 2011 at 3:55 PM, Shirley Ma <mashirle@...ibm.com> wrote:
> Resubmit it with a typo fix.
>
> Signed-off-by: Shirley Ma <xma@...ibm.com>
> ---
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 0c7321c..c8201d4 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -429,6 +429,22 @@ static int add_recvbuf_mergeable(struct virtnet_info *vi, gfp_t gfp)
>        return err;
>  }
>
> +static int fill_one(struct virtnet_info *vi, gfp_t gfp)
> +{
> +       int err;
> +
> +       if (vi->mergeable_rx_bufs)
> +               err = add_recvbuf_mergeable(vi, gfp);
> +       else if (vi->big_packets)
> +               err = add_recvbuf_big(vi, gfp);
> +       else
> +               err = add_recvbuf_small(vi, gfp);
> +
> +       if (err >= 0)
> +               ++vi->num;
> +       return err;
> +}
> +
>  /* Returns false if we couldn't fill entirely (OOM). */
>  static bool try_fill_recv(struct virtnet_info *vi, gfp_t gfp)
>  {
> @@ -436,17 +452,10 @@ static bool try_fill_recv(struct virtnet_info *vi, gfp_t gfp)
>        bool oom;
>
>        do {
> -               if (vi->mergeable_rx_bufs)
> -                       err = add_recvbuf_mergeable(vi, gfp);
> -               else if (vi->big_packets)
> -                       err = add_recvbuf_big(vi, gfp);
> -               else
> -                       err = add_recvbuf_small(vi, gfp);
> -
> +               err = fill_one(vi, gfp);
>                oom = err == -ENOMEM;
>                if (err < 0)
>                        break;
> -               ++vi->num;
>        } while (err > 0);
>        if (unlikely(vi->num > vi->max))
>                vi->max = vi->num;
> @@ -506,13 +515,13 @@ again:
>                receive_buf(vi->dev, buf, len);
>                --vi->num;
>                received++;
> -       }
> -
> -       if (vi->num < vi->max / 2) {
> -               if (!try_fill_recv(vi, GFP_ATOMIC))
> +               if (fill_one(vi, GFP_ATOMIC) < 0)
>                        schedule_delayed_work(&vi->refill, 0);
>        }
>
> +       /* notify buffers are refilled */
> +       virtqueue_kick(vi->rvq);
> +

How does this reduce latency?   We are doing the same amount of work
in both cases, and in both cases the newly available buffers are not
visible to the device until the virtqueue_kick..


>        /* Out of packets? */
>        if (received < budget) {
>                napi_complete(napi);
>
>
> --
> To unsubscribe from this list: send the line "unsubscribe kvm" in
> the body of a message to majordomo@...r.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html