On Thu, 29 Nov 2012 13:30:13 +0200 "Michael S. Tsirkin" <mst@xxxxxxxxxx> wrote: > On Thu, Nov 29, 2012 at 06:13:13PM +0800, Jason Wang wrote: > > On Wednesday, November 28, 2012 08:53:05 AM Stephen Hemminger wrote: > > > On Wed, 28 Nov 2012 14:48:52 +0800 > > > > > > Jason Wang <jasowang@xxxxxxxxxx> wrote: > > > > On 11/28/2012 12:49 AM, Stephen Hemminger wrote: > > > > > On Tue, 27 Nov 2012 14:45:13 +0800 > > > > > > > > > > Jason Wang <jasowang@xxxxxxxxxx> wrote: > > > > >> On 11/27/2012 01:37 AM, Stephen Hemminger wrote: > > > > >>> On Mon, 26 Nov 2012 15:56:52 +0800 > > > > >>> > > > > >>> Jason Wang <jasowang@xxxxxxxxxx> 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 <jasowang@xxxxxxxxxx> > > > > >>> > > > > >>> 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 majordomo@xxxxxxxxxxxxxxx > > > > >>> 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. > > Timer would prevent complete deadlock but it is very expensive > in the virt scenario. > pulling at ring half full would only help if ring gets half full :) > which it does not have to. A timer that fires once (when idle) to mop up the last packet in a stream would be not very expensive. Most of the time, it would just be continually rescheduled. _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
