Avi Kivity wrote: > Richard Davies wrote: > > Hi Avi, > > > > Thanks to you and several others for offering help. We will work with Avi at > > first, but are grateful for all the other offers of help. We have a number > > of other qemu-related projects which we'd be interested in getting done, and > > will get in touch with these names (and anyone else who comes forward) to > > see if any are of interest to you. > > > > > > This slow boot problem is intermittent and varys in how slow the boots are, > > but I managed to trigger it this morning with medium slow booting (5-10 > > minutes) and link to the requested traces below. > > > > The host in question has 128GB RAM and dual AMD Opteron 6128 (16 cores > > total). It is running kernel 3.5.1 and qemu-kvm 1.1.1. > > > > In this morning's test, we have 3 guests, all booting Windows with 40GB RAM > > and 8 cores each (we have seen small VMs go slow as I originally said, but > > it is easier to trigger with big VMs): > > > > pid 15665: qemu-kvm -nodefaults -m 40960 -smp 8 -cpu host,hv_relaxed \ > > -vga cirrus -usbdevice tablet -vnc :99 -monitor stdio -hda test1.raw > > pid 15676: qemu-kvm -nodefaults -m 40960 -smp 8 -cpu host,hv_relaxed \ > > -vga cirrus -usbdevice tablet -vnc :98 -monitor stdio -hda test2.raw > > pid 15653: qemu-kvm -nodefaults -m 40960 -smp 8 -cpu host,hv_relaxed \ > > -vga cirrus -usbdevice tablet -vnc :97 -monitor stdio -hda test3.raw > > > > We are running with hv_relaxed since this was suggested in the previous > > thread, but we see intermittent slow boots with and without this flag. > > > > > > All 3 VMs are booting slowly for most of the attached capture, which I > > started after confirming the slow boots and stopped as soon as the first of > > them (15665) had booted. In terms of visible symptoms, the VMs are showing > > the Windows boot progress bar, which is moving very slowly. In top, the VMs > > are at 400% CPU and their resident state size (RES) memory is slowly > > counting up until it reaches the full VM size, at which point they finish > > booting. > > > > > > Here are the trace files: > > > > http://users.org.uk/slow-win-boot-1/ps.txt (ps auxwwwf as root) > > http://users.org.uk/slow-win-boot-1/top.txt (top with 2 VMs still slow) > > http://users.org.uk/slow-win-boot-1/trace-console.txt (running trace-cmd) > > http://users.org.uk/slow-win-boot-1/trace.dat (the 1.7G trace data file) > > http://users.org.uk/slow-win-boot-1/trace-report.txt (the 4G trace report) > > > > > > Please let me know if there is anything else which I can provide? > > > There are tons of PAUSE exits indicating cpu overcommit (and indeed you > are overcommitted by about 50%). > > What host kernel version are you running? > > Does this reproduce without overcommit? We're running host kernel 3.5.1 and qemu-kvm 1.1.1. I hadn't though about it, but I agree this is related to cpu overcommit. The slow boots are intermittent (and infrequent) with cpu overcommit whereas I don't think it occurs without cpu overcommit. In addition, if there is a slow boot ongoing, and you kill some other VMs to reduce cpu overcommit then this will sometimes speed it up. I guess the question is why even with overcommit most boots are fine, but some small fraction then go slow? Richard. -- 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
