On Fri, Jan 14, 2011 at 06:58:18AM +0200, Michael S. Tsirkin wrote: > On Fri, Jan 14, 2011 at 08:41:36AM +0900, Simon Horman wrote: > > On Thu, Jan 13, 2011 at 10:45:38AM -0500, Jesse Gross wrote: > > > On Thu, Jan 13, 2011 at 1:47 AM, Simon Horman <horms@xxxxxxxxxxxx> wrote: > > > > On Mon, Jan 10, 2011 at 06:31:55PM +0900, Simon Horman wrote: > > > >> On Fri, Jan 07, 2011 at 10:23:58AM +0900, Simon Horman wrote: > > > >> > On Thu, Jan 06, 2011 at 05:38:01PM -0500, Jesse Gross wrote: > > > >> > > > > >> > [ snip ] > > > >> > > > > > >> > > I know that everyone likes a nice netperf result but I agree with > > > >> > > Michael that this probably isn't the right question to be asking. ÂI > > > >> > > don't think that socket buffers are a real solution to the flow > > > >> > > control problem: they happen to provide that functionality but it's > > > >> > > more of a side effect than anything. ÂIt's just that the amount of > > > >> > > memory consumed by packets in the queue(s) doesn't really have any > > > >> > > implicit meaning for flow control (think multiple physical adapters, > > > >> > > all with the same speed instead of a virtual device and a physical > > > >> > > device with wildly different speeds). ÂThe analog in the physical > > > >> > > world that you're looking for would be Ethernet flow control. > > > >> > > Obviously, if the question is limiting CPU or memory consumption then > > > >> > > that's a different story. > > > >> > > > > >> > Point taken. I will see if I can control CPU (and thus memory) consumption > > > >> > using cgroups and/or tc. > > > >> > > > >> I have found that I can successfully control the throughput using > > > >> the following techniques > > > >> > > > >> 1) Place a tc egress filter on dummy0 > > > >> > > > >> 2) Use ovs-ofctl to add a flow that sends skbs to dummy0 and then eth1, > > > >> Â Âthis is effectively the same as one of my hacks to the datapath > > > >> Â Âthat I mentioned in an earlier mail. The result is that eth1 > > > >> Â Â"paces" the connection. > > This is actually a bug. This means that one slow connection will affect > fast ones. I intend to change the default for qemu to sndbuf=0 : this > will fix it but break your "pacing". So pls do not count on this > behaviour. Do you have a patch I could test? > > > > Further to this, I wonder if there is any interest in providing > > > > a method to switch the action order - using ovs-ofctl is a hack imho - > > > > and/or switching the default action order for mirroring. > > > > > > I'm not sure that there is a way to do this that is correct in the > > > generic case. It's possible that the destination could be a VM while > > > packets are being mirrored to a physical device or we could be > > > multicasting or some other arbitrarily complex scenario. Just think > > > of what a physical switch would do if it has ports with two different > > > speeds. > > > > Yes, I have considered that case. And I agree that perhaps there > > is no sensible default. But perhaps we could make it configurable somehow? > > The fix is at the application level. Run netperf with -b and -w flags to > limit the speed to a sensible value. Perhaps I should have stated my goals more clearly. I'm interested in situations where I don't control the application. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
