On Thu, Apr 12, 2012 at 02:21:06PM -0400, Rik van Riel wrote: > On 04/11/2012 01:21 PM, Chegu Vinod wrote: > > > >Hello, > > > >While running an AIM7 (workfile.high_systime) in a single 40-way (or a single > >60-way KVM guest) I noticed pretty bad performance when the guest was booted > >with 3.3.1 kernel when compared to the same guest booted with 2.6.32-220 > >(RHEL6.2) kernel. > > >For the 40-way Guest-RunA (2.6.32-220 kernel) performed nearly 9x better than > >the Guest-RunB (3.3.1 kernel). In the case of 60-way guest run the older guest > >kernel was nearly 12x better ! > How many CPUs your host has? > >Turned on function tracing and found that there appears to be more time being > >spent around the lock code in the 3.3.1 guest when compared to the 2.6.32-220 > >guest. > > Looks like you may be running into the ticket spinlock > code. During the early RHEL 6 days, Gleb came up with a > patch to automatically disable ticket spinlocks when > running inside a KVM guest. > > IIRC that patch got rejected upstream at the time, > with upstream developers preferring to wait for a > "better solution". > > If such a better solution is not on its way upstream > now (two years later), maybe we should just merge > Gleb's patch upstream for the time being? I think the pv spinlock that is actively discussed currently should address the issue, but I am not sure someone tests it against non-ticket lock in a guest to see which one performs better. -- Gleb. -- 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
