On Wed, 2019-06-26 at 20:41 +0200, Thomas Gleixner wrote: > On Wed, 26 Jun 2019, Konrad Rzeszutek Wilk wrote: > > > > On Wed, Jun 26, 2019 at 06:16:08PM +0200, Peter Zijlstra wrote: > > > > > > On Wed, Jun 26, 2019 at 10:54:13AM -0400, Konrad Rzeszutek Wilk wrote: > > > > > > > > There were some ideas that Ankur (CC-ed) mentioned to me of using the perf > > > > counters (in the host) to sample the guest and construct a better > > > > accounting idea of what the guest does. That way the dashboard > > > > from the host would not show 100% CPU utilization. > > > > > > But then you generate extra noise and vmexits on those cpus, just to get > > > this accounting sorted, which sounds like a bad trade. > > > > Considering that the CPUs aren't doing anything and if you do say the > > IPIs "only" 100/second - that would be so small but give you a big benefit > > in properly accounting the guests. > > The host doesn't know what the guest CPUs are doing. And if you have a full > zero exit setup and the guest is computing stuff or doing that network > offloading thing then they will notice the 100/s vmexits and complain. If the host is completely in no_full_hz mode and the pCPU is dedicated to a single vCPU/task (and the guest is 100% CPU bound and never exits), you would still be ticking in the host once every second for housekeeping, right? Would not updating the mwait-time once a second be enough here? > > > > > But perhaps there are other ways too to "snoop" if a guest is sitting on > > an MWAIT? > > No idea. > > Thanks, > > tglx > > Amazon Development Center Germany GmbH Krausenstr. 38 10117 Berlin Geschaeftsfuehrung: Christian Schlaeger, Ralf Herbrich Eingetragen am Amtsgericht Charlottenburg unter HRB 149173 B Sitz: Berlin Ust-ID: DE 289 237 879
