lkml.org 
[lkml]   [2006]   [May]   [15]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] tcpdump may trace some outbound packets twice.
On Mon, 15 May 2006 16:11:05 -0700 (PDT)
Ranjit Manomohan <ranjitm@google.com> wrote:

> On Mon, 15 May 2006, David S. Miller wrote:
>
> > From: Ranjit Manomohan <ranjitm@google.com>
> > Date: Mon, 15 May 2006 14:19:06 -0700 (PDT)
> >
> > > Heres a new version which does a copy instead of the clone to avoid
> > > the double cloning issue.
> >
> > I still very much dislike this patch because it is creating
> > 1 more clone per packet than is actually necessary and that
> > is very expensive.
> >
> > dev_queue_xmit_nit() is going to clone whatever SKB you send into
> > there, so better to just bump the reference count (with skb_get())
> > instead of cloning or copying.
> >
>
> I was a bit apprehensive about just incrementing the refcnt but that works
> too. Attached is the modified version.
>
> -Thanks,
> Ranjit
>
> --- linux-2.6/net/sched/sch_generic.c 2006-05-10 12:34:52.000000000 -0700
> +++ linux/net/sched/sch_generic.c 2006-05-15 15:48:03.000000000 -0700
> @@ -136,8 +136,12 @@
>
> if (!netif_queue_stopped(dev)) {
> int ret;
> + struct sk_buff *skbc = NULL;
> + /* Increment the reference count on the skb so
> + * that we can use it after a successful xmit.
> + */
> if (netdev_nit)
> - dev_queue_xmit_nit(skb, dev);
> + skbc = skb_get(skb);

skbc = netdev_nit ? skb_get(skb) : NULL;
>
> ret = dev->hard_start_xmit(skb, dev);
> if (ret == NETDEV_TX_OK) {
> @@ -145,9 +149,20 @@
> dev->xmit_lock_owner = -1;
> spin_unlock(&dev->xmit_lock);
> }
> + if (skbc) {
> + /* transmit succeeded,
> + * trace the buffer. */
> + dev_queue_xmit_nit(skbc,dev);
> + kfree_skb(skbc);
> + }
> spin_lock(&dev->queue_lock);
> return -1;
> }
> +
> + /* Call free in case we incremented refcnt */
> + if (skbc)
> + kfree_skb(skbc);

kfree_skb(NULL) is legal so the conditional here is unneeded.

But the increased calls to kfree_skb(NULL) would probably bring the
"unlikely()" hordes descending on kfree_skb, so maybe:

if (unlikely(netdev_nit))
kfree_skb(skbc);

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2006-05-16 01:43    [from the cache]
©2003-2011 Jasper Spaans