Mark McLoughlin wrote: > virtio_net currently only frees old transmit skbs just > before queueing new ones. If the queue is full, it then > enables interrupts and waits for notification that more > work has been performed. > > However, a side-effect of this scheme is that there are > always xmit skbs left dangling when no new packets are > sent, against the Documentation/networking/driver.txt > guideline: > > "... it is not allowed for your TX mitigation scheme > to let TX packets "hang out" in the TX ring unreclaimed > forever if no new TX packets are sent." > > Add a timer to ensure that any time we queue new TX > skbs, we will shortly free them again. > > This fixes an easily reproduced hang at shutdown where > iptables attempts to unload nf_conntrack and nf_conntrack > waits for an skb it is tracking to be freed, but virtio_net > never frees it. > Sorry to barge in late, but IMO the timer should be on the host, which is cheaper than on the guest (well, a 100ms timer is likely zero cost, but I still don't like it). the host should fire a tx completion interrupt whenever the completion queue has "enough" entries, where we can define "enough" now as the halfway mark or a timer expiry, whichever comes earlier. We can later improve "enough" to be "just enough so the timer never triggers" and adjust it dynamically. It probably doesn't matter for Linux, but I don't want to punish guests that can do true async networking and depend on timely completion notification. -- error compiling committee.c: too many arguments to function _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/virtualization
