On Wednesday, November 28, 2012 08:53:05 AM Stephen Hemminger wrote: > On Wed, 28 Nov 2012 14:48:52 +0800 > > Jason Wang <jasow...@redhat.com> wrote: > > On 11/28/2012 12:49 AM, Stephen Hemminger wrote: > > > On Tue, 27 Nov 2012 14:45:13 +0800 > > > > > > Jason Wang <jasow...@redhat.com> wrote: > > >> On 11/27/2012 01:37 AM, Stephen Hemminger wrote: > > >>> On Mon, 26 Nov 2012 15:56:52 +0800 > > >>> > > >>> Jason Wang <jasow...@redhat.com> wrote: > > >>>> Some deivces do not free the old tx skbs immediately after it has > > >>>> been sent > > >>>> (usually in tx interrupt). One such example is virtio-net which > > >>>> optimizes for virt and only free the possible old tx skbs during the > > >>>> next packet sending. This would lead the pktgen to wait forever in > > >>>> the refcount of the skb if no other pakcet will be sent afterwards. > > >>>> > > >>>> Solving this issue by introducing a new flag IFF_TX_SKB_FREE_DELAY > > >>>> which could notify the pktgen that the device does not free skb > > >>>> immediately after it has been sent and let it not to wait for the > > >>>> refcount to be one. > > >>>> > > >>>> Signed-off-by: Jason Wang <jasow...@redhat.com> > > >>> > > >>> Another alternative would be using skb_orphan() and skb->destructor. > > >>> There are other cases where skb's are not freed right away. > > >>> -- > > >>> To unsubscribe from this list: send the line "unsubscribe netdev" in > > >>> the body of a message to majord...@vger.kernel.org > > >>> More majordomo info at http://vger.kernel.org/majordomo-info.html > > >> > > >> Hi Stephen: > > >> > > >> Do you mean registering a skb->destructor for pktgen then set and check > > >> bits in skb->tx_flag? > > > > > > Yes. Register a destructor that does something like update a counter > > > (number of packets pending), then just spin while number of packets > > > pending is over threshold. > > > -- > > > > Not sure this is the best method, since pktgen was used to test the tx > > process of the device driver and NIC. If we use skb_orhpan(), we would > > miss the test of tx completion part. > > There are other places that delay freeing and your solution would mean > finding and fixing all those. Code that does that already has to use > skb_orphan() to work, and I was looking for a way that could use that. > Introducing another flag value seems like a long term burden. >
Get the point, will draft another version. > Alternatively, virtio could do cleanup more aggressively. Maybe in response > to ring getting half full, or add a cleanup timer or something to avoid the > problem. May worth to try. Another method is that virtio has a feature to notify guest when tx ring is empty, we could free the old tx skbs there. But it may brings extra overhead. If we could let virtio_net free the old tx skb timely, it would be easier to bring BQL support to virtio_net also. Thanks > > > > -- > To unsubscribe from this list: send the line "unsubscribe netdev" in > the body of a message to majord...@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
