Gregory Haskins wrote: > Jan Kiszka wrote: >> Hi, >> >> did anyone recently tried current KVM for Intel over some real-time >> Linux? I'm seeing more than 500 us latency peaks on the host, >> specifically during VM startup. This applies to both 2.6.29.6-rt23 and >> Xenomai/I-pipe. For -rt, I both tried the included (patched) KVM modules >> as well as kvm.git head with some additionally required -rt fixes. >> Xenomai ran over a 2.6.30 kernel with my own KVM-enabler patch. >> >> Early instrumentation actually points to the guest exit itself: I added >> markers right before and after the assembly part of vmx_vcpu_run, and >> further instrumentation reports that the next host APIC tick should go >> off right inside guest mode. But KVM leaves the switching part 500 us >> too late in that case - as if guest exit on external IRQs was disabled. >> >> Will debug this further, but I'm also curious to hear other user >> experiences. >> >> Jan >> >> > Hi Jan, > Did you try to run with latency-tracer enabled? If not, this may > pinpoint the source for you. I did, see above. It finally turned out that I got burned once again by wbinvd: My test CPUs (and likely also some of my customer) are too "old" to support SECONDARY_VM_EXEC_CONTROL, which includes trapping guest's wbinvd invocations. Too bad. I vaguely recall that someone promised to add a feature reporting facility for all those nice things, modern VM-extensions may or may not support (something like or even an extension of /proc/cpuinfo). What is the state of this plan? Would be specifically interesting for Intel CPUs as there seem to be many of them out there with restrictions for special use cases - like real-time. Jan (who is now patching his guest to avoid wbinvd where possible) -- Siemens AG, Corporate Technology, CT SE 2 Corporate Competence Center Embedded Linux -- 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
