* Jan Kiszka <jan.kiszka@xxxxxxxxxxx> wrote: > Jes Sorensen wrote: > > Hi, > > > > It looks like several of us have been looking at how to use the PMU > > for virtualization. Rather than continuing to have discussions in > > smaller groups, I think it is a good idea we move it to the mailing > > lists to see what we can share and avoid duplicate efforts. > > > > There are really two separate things to handle: > > > > 1) Add support to perf to allow it to monitor a KVM guest from the > > host. > > > > 2) Allow guests access to the PMU (or an emulated PMU), making it > > possible to run perf on applications running within the guest. > > > > I know some of you have been looking at 1) and I am currently working > > on 2). I have been looking at various approaches, including whether it > > is feasible to share the PMU between the host and multiple guests. For > > now I am going to focus on allowing one guest to take control of the > > PMU, then later hopefully adding support for multiplexing it between > > multiple guests. > > Given that perf can apply the PMU to individual host tasks, I don't see > fundamental problems multiplexing it between individual guests (which can > then internally multiplex it again). In terms of how to expose it to guests, a 'soft PMU' might be a usable approach. Although to Linux guests you could expose much more functionality and an non-PMU-limited number of instrumentation events, via a more intelligent interface. But note that in terms of handling it on the host side the PMU approach is not acceptable: instead it should map to proper perf_events, not try to muck with the PMU itself. That, besides integrating properly with perf usage on the host, will also allow interesting 'PMU' features on guests: you could set up the host side to trace block IO requests (or VM exits) for example, and expose that as 'PMC #0' on the guest side. That's a neat feature: the guest profiling tools would immediately (and transparently) be able to measure VM exits or IO heaviness, on a per guest basis, as seen on the host side. More would be possible too. Thanks, Ingo -- 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
