On 03/05/2018 14:02, Alexander Shishkin wrote: > I don't see why. System-wide tracing takes place while perf record is > running. When it's done, it's done and we can un-disable the guest > tracing, without requiring the user to kill all their VMs and reload > modules. Guest tracing can only be enabled at boot time, because the guest's CPUID changes depending on whether it's enabled. And likewise if perf record can do system-wide tracing at any time during the guest's execution, we need to know it at boot time in order to set the guest CPUID. Paolo
