On Fri, 2009-05-29 at 23:46 +0930, Rusty Russell wrote: > The virtio_net driver is complicated by the two methods of freeing old > xmit buffers (in addition to freeing old ones at the start of the xmit > path). > > The original code used a 1/10 second timer attached to xmit_free(), > reset on every xmit. Before we orphaned skbs on xmit, the > transmitting userspace could block with a full socket until the timer > fired, the skb destructor was called, and they were re-woken.
The timer was actually added to solve a hang when trying to unload nf_conntrack AFAIR - nf_conntrack was blocking on the skb being freed and we never actually freed it. I think skb_orphan() is enough to prevent this, is it? > So we added the VIRTIO_F_NOTIFY_ON_EMPTY feature: supporting devices > send an interrupt (even if normally suppressed) on an empty xmit ring > which makes us schedule xmit_tasklet(). This was a benchmark win. > > Unfortunately, VIRTIO_F_NOTIFY_ON_EMPTY makes quite a lot of work: a > host which is faster than the guest will fire the interrupt every xmit > packet (slowing the guest down further). Ouch. So, does simply disabling host support for VIRTIO_F_NOTIFY_ON_EMPTY speed up current guests? Cheers, Mark. _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linux-foundation.org/mailman/listinfo/virtualization
