Ryan Harper wrote: > * Anthony Liguori <[EMAIL PROTECTED]> [2008-05-12 15:05]: > >> Ryan Harper wrote: >> >>> I've been digging into some of the instability we see when running >>> larger numbers of guests at the same time. The test I'm currently using >>> involves launching 64 1vcpu guests on an 8-way AMD box. >>> >> Note this is a Barcelona system and therefore should have a >> fixed-frequency TSC. >> >> >>> With the latest >>> kvm-userspace git and kvm.git + Gerd's kvmclock fixes, I can launch all >>> 64 of these 1 second apart, >>> >> BTW, what if you don't pace-out the startups? Do we still have issues >> with that? >> > > Do you mean without the 1 second delay or with a longer delay? My > experience is that delay helps (fewer hangs), but doesn't solve things > completely. >
So you see problems when using numactrl to pin and using a 0-second delay? The short delay may help reduce the number of CPU migrations which would explain your observation. If there are problems when doing a 0-second delay and numactl, then perhaps it's not just a cpu-migration issue. > In svm.c, I do think we account for most of that time since the delta > calculation will shift the guest time forward to the tsc value read in > svm_vcpu_load(). We'll still miss the time between fixing the offset > and when the guest can actually read its tsc. > Yes, which is the duration that the guest isn't scheduled on any processor and the next time it runs happens to be on a different process. >> A possible way to fix this (that's only valid on a processor with a >> fixed-frequency TSC), is to take a high-res timestamp on vcpu_put, and >> then on vcpu_load, take the delta timestamp since the old TSC was saved, >> and use the TSC frequency on the new pcpu to calculate the number of >> elapsed cycles. >> >> Assuming a fixed frequency TSC, and a calibrated TSC across all >> processors, you could get the same affects by using the VT tsc delta >> logic. Basically, it always uses the new CPU's TSC unless that would >> cause the guest to move backwards in time. As long as you have a >> stable, calibrated TSC, this would work out. >> >> Can you try your old patch that did this and see if it fixes the problem? >> > > Yeah, I'll give it a spin. > Thanks, Anthony Liguori ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ _______________________________________________ kvm-devel mailing list kvm-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kvm-devel
