On Tue, 19 May 2009 12:10:13 pm David Miller wrote: > From: Rusty Russell <ru...@rustcorp.com.au> > Date: Mon, 18 May 2009 22:18:47 +0930 > > We check for finished xmit skbs on every xmit, or on a timer (unless > > the host promises to force an interrupt when the xmit ring is empty). > > This can penalize userspace tasks which fill their sockbuf. Not much > > difference with TSO, but measurable with large numbers of packets. > > > > There are a finite number of packets which can be in the transmission > > queue. We could fire the timer more than every 100ms, but that would > > just hurt performance for a corner case. This seems neatest. ... > > Signed-off-by: Rusty Russell <ru...@rustcorp.com.au> > > If this is so great for virtio it would also be a great idea > universally, but we don't do it. > > What you're doing by orphan'ing is creating a situation where a single > UDP socket can loop doing sends and monopolize the TX queue of a > device. The only control we have over a sender for fairness in > datagram protocols is that send buffer allocation.
Urgh, that hadn't even occurred to me. Good point. > I'm guilty of doing this too in the NIU driver, also because there I > lack a "TX queue empty" interrupt and this can keep TCP sockets from > getting stuck. > > I think we need a generic solution to this issue because it is getting > quite common to see cases where the packets in the TX queue of a > device can sit there indefinitely. I haven't thought this through properly, but how about a hack where we don't orphan packets if the ring is over half full? Then I guess we could overload the watchdog as a more general timer-after-no- xmit? Rusty. _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linux-foundation.org/mailman/listinfo/virtualization
