Hi Peter, Any comments?
Thanks, Kan > Subject: RE: [PATCH V3 0/6] export perf overheads information (kernel) > > > Ping. > Any comments for the series? > > Thanks, > Kan > > > Subject: [PATCH V3 0/6] export perf overheads information (kernel) > > > > From: Kan Liang <kan.li...@intel.com> > > > > This series only include the kernel related patches. > > > > Profiling brings additional overhead. High overhead may impacts the > > behavior of the profiling object, impacts the accuracy of the > > profiling result, and even hang the system. > > Currently, perf has dynamic interrupt throttle mechanism to lower the > > sample rate and overhead. But it has limitations. > > - The mechanism only focus in the sampling overhead. However, there > > are other parts which also bring big overhead. E.g, multiplexing. > > - The hint from the mechanism doesn't work on fixed period. > > - The system changes which caused by the mechanism are not recorded > > in the perf.data. Users have no idea about the overhead and its > > impact. > > Actually, any passive ways like dynamic interrupt throttle mechanism > > are only palliative. The best way is to export overhead information, > > provide more hints, and help the users design more proper perf > command. > > > > For kernel, three parts can bring obvious overhead. > > - sample overhead: For x86, it's the time cost in perf NMI handler. > > - multiplexing overhead: The time cost spends on rotate context. > > - side-band events overhead: The time cost spends on iterating all > > events that need to receive side-band events. > > The time cost of those parts are stored in pmu's per-cpu cpuctx. > > The tool can call PERF_EVENT_IOC_STAT when it's 'done'. Then the > > kernel generates the overhead record PERF_RECORD_OVERHEAD. > > > > User can use the overhead information to refine their perf command and > > get accurate profiling result. For example, if there is high overhead > > warning, user may reduce the number of events/increase the > > period/decrease the frequency. > > Developer can also use the overhead information to find bugs. > > > > Changes since V2: > > - Separate kernel patches from the previous version > > - Add PERF_EVENT_IOC_STAT to control overhead statistics > > - Collect per pmu overhead information > > - Store the overhead information in pmu's cpuctx > > - Add CPU information in overhead record > > > > Changes since V1: > > - fix u32 holes and remove duplicate CPU information > > - configurable overhead logging > > - Introduce the concept of PMU specific overhead and common core > > overhead. Rename NMI overhead to PMU sample overhead > > - Add log_overhead in perf_event_context to indicate the logging of > > overhead > > - Refine the output of overhead information > > - Use perf CPU time to replace perf write data overhead > > - Refine the formula of overhead evaluation > > - Refine perf script > > > > Kan Liang (6): > > perf/core: Introduce PERF_RECORD_OVERHEAD > > perf/core: Add PERF_EVENT_IOC_STAT to control overhead statistics > > perf/x86: implement overhead stat for x86 pmu > > perf/core: calculate multiplexing overhead > > perf/core: calculate side-band events overhead > > perf/x86: calculate sampling overhead > > > > arch/x86/events/core.c | 45 +++++++++++++++++++++++- > > include/linux/perf_event.h | 12 +++++++ > > include/uapi/linux/perf_event.h | 44 ++++++++++++++++++++++- > > kernel/events/core.c | 77 > > ++++++++++++++++++++++++++++++++++++++++- > > 4 files changed, 175 insertions(+), 3 deletions(-) > > > > -- > > 2.4.3
