* Zhang, Yanmin <yanmin_zhang@xxxxxxxxxxxxxxx> wrote: > On Thu, 2010-02-25 at 17:26 +0100, Ingo Molnar wrote: > > * 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. > > So virtualization becomes non-transparent to guest os? I know virtio is an > optimization on guest side. The 'soft PMU' is transparent. The 'count IO events' kind of feature could be transparent too: you could re-configure (on the host) a given 'hardware' event to really count some software event. That would make it compatible with whatever guest side tooling (without having to change that tooling) - while still allowing interesting new things to be measured. 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
