Hi Mike, On Wed, Feb 03, 2021 at 05:39:54PM +0000, Mike Leach wrote: [...] > > +2.2) Tracing PID > > + > > +When the kernel is running at EL2 with Virtualization Host Extensions (VHE), > > +perf records CONTEXTIDR_EL2 in the trace data and can be used as PID when > > +decoding; and if the kernel is running at EL1 with nVHE, CONTEXTIDR_EL1 is > > +traced for PID. > > + > > Would this introductory paragraph be better if is explained where the > kernel stores the PID for the different levels, then we logically move > on to how to trace this in perf. > > e.g:- > > "The lernel can be built to write the PID value into the PE ContextID registers. > For a kernel running at EL1, the PID is stored in CONTEXTIDR_EL1. > A PE may implement ARM Virtualisation Host Extensions (VHE), were the > kernel can run at EL2 as a virtualisation host. > In this case the PID value is stored in CONTEXTIDR_EL2. > perf provides PMU options which program the ETM to insert these values > into the trace data." Will in next spin; thanks a lot for writing up! > > +To support tracing PID for the kernel runs at different exception levels, > > +the PMU formats are defined as follow: > > + > > + "contextid1": Available on both EL1 kernel and EL2 kernel. When the > > + kernel is running at EL1, "contextid1" enables the PID > > + tracing; when the kernel is running at EL2, this enables > > + tracing the PID of guest applications. > > + > > + "contextid2": Only usable when the kernel is running at EL2. When > > + selected, enables PID tracing on EL2 kernel. > > + > > + "contextid": Will be an alias for the option that enables PID > > + tracing. I.e, > > + contextid == contextid1, on EL1 kernel. > > + contextid == contextid2, on EL2 kernel. > > + > > +The perf tool automatically sets corresponding bit for the "contextid" config, > > +therefore, the user doesn't have to bother which EL the kernel is running. > > + > > + i.e, perf record -e cs_etm/contextid/u -- uname > > + or perf record -e cs_etm//u -- uname > > + > > +will always do the "PID" tracing, independent of the kernel EL. > > + > > This is telling me that both cs_etm// and cs_etm/contextid/ have the > same effect - trace PID. Is this correct? Correct. > If so, then contextid, contextid1 and contextid2 have no effect except > in specific EL2 circumstances. Yes, exactly. Thanks, Leo > > +When the kernel is running at EL2 with VHE, if user wants to trace both the > > +PIDs for both host and guest, the two configs "contextid1" and "contextid2" > > +can be set at the same time: > > + > > + perf record -e cs_etm/contextid1,contextid2/u -- uname > > + > > > > > Regards > > Mike > > > > Generating coverage files for Feedback Directed Optimization: AutoFDO > > --------------------------------------------------------------------- > > -- > > 2.25.1 > > > > > -- > Mike Leach > Principal Engineer, ARM Ltd. > Manchester Design Centre. UK
