[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] Paravirtualised drivers for fully virtualised domains, rev9
On Fri, 2006-08-11 at 11:17 +0100, Steven Smith wrote: > > Here is what I have found so far in trying to chase down the cause of the > > slowdown. > > The qemu-dm process is running 99.9% of the CPU on dom0. > That seems very wrong. When I try this, the device model is almost > completely idle. Could you see what strace says, please, or if there > are any strange messages in the /var/log/qemu-dm. file? I haven't tried the patches being discussed in this thread but I'm seeing similar problems with qemu-dm anyway... I've been looking into bugzilla 725 and I'm also seeing 100% cpu usage by qemu-dm. xm-test uses the nographic flag and I find that if this is not set then the cpu usage drops to normal levels and the test passes. > > > It appears that a lot of time is spent running timers and getting the > > current time. Yes, this is what I was seeing with the nographic flag set. > Not being familiar with the code, I am now crawling through > > it to see how timers are handled and how the xen-vnif PV driver uses them. > Timer handling isn't really changed by any of these patches. Patch > 02.ioemu_xen_evtchns.diff is in vaguely the same area, but I can't see > how it could cause the problems you're seeing, assuming your > hypervisor and libxc are up to date. > > What changeset of xen-unstable did you apply the patches to? I've been seeing the problem on recent unstable changesets without the patches. Changesets 10992, 10949 for example. > > > P.S. This just in from a test running while I typed the above. I noticed > > that qemu will start a "gui_timer" when VNC is not used. I normally run > > without graphics (nographic=1 in the domain config file). > I changed the > > config file to use VNC. The qemu-dm CPU utilization in dom0 dropped to > > below 10%. Yep, that's what I see without the patches. > The network performance improved from 0.19 Mb/s to 9.75 Mb/s > > (still less than the 23.07 Mb/s for a fully virtualized domain). > When I try this, I see about 1600Mb/s between dom0 and a > paravirtualised domU, about 30Mb/s between dom0 and an ioemu domU, and > about 1200Mb/s between dom0 and an HVM domU running these drivers, all > collected using netpipe-tcp. That is a regression, but much smaller > than you're seeing. > > There are a couple of obvious things to check: > > 1) Do the statistics reported by ifconfig show any errors? > 2) How often is the event channel interrupt firing according to > /proc/interrupts? I see about 50k-150k/second. > 3) Is there any packet loss when you ping a domain? Start your test > and run a ping in parallel. > > The other thing is that these drivers seem to be very sensitive to > kernel debugging options in the domU. If you've got anything enabled > in the kernel hacking menu it might be worth trying again with that > switched off. > > > It appears there is some interaction between using the xen-vnif > > driver and the qemu timer code. I'm still exploring. > I'd be happier if I could reproduce this problem here. Are you > running SMP? PAE? 64 bit? What kernel are you running in the domU? > > Steven. > _______________________________________________ > Xen-devel mailing list > Xen-devel@xxxxxxxxxxxxxxxxxxx > http://lists.xensource.com/xen-devel _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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