On Tue, Feb 02, 2021 at 11:24:48PM +0000, Suzuki Kuruppassery Poulose wrote: > On 2/2/21 4:38 PM, Leo Yan wrote: > > After support the PID tracing for the kernel in EL1 or EL2, the usage > > gets more complicated. > > > > This patch gives description for the PMU formats of contextID configs, > > this can help users to understand how to control the knobs for PID > > tracing when the kernel is in different ELs. > > > > Signed-off-by: Leo Yan <leo.yan@xxxxxxxxxx> > > --- > > Documentation/trace/coresight/coresight.rst | 37 +++++++++++++++++++++ > > 1 file changed, 37 insertions(+) > > > > diff --git a/Documentation/trace/coresight/coresight.rst b/Documentation/trace/coresight/coresight.rst > > index 0b73acb44efa..771558f22938 100644 > > --- a/Documentation/trace/coresight/coresight.rst > > +++ b/Documentation/trace/coresight/coresight.rst > > @@ -512,6 +512,43 @@ The --itrace option controls the type and frequency of synthesized events > > Note that only 64-bit programs are currently supported - further work is > > required to support instruction decode of 32-bit Arm programs. > > +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. > > + > > +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. > > + > > +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 > > + > > To make this case clear, we could change the command from uname to > something like: > > perf record -e cs_etm/contextid1,contextid2/u -- vm Exactly, will refine. > Otherwise looks good to me. > > With the above fixed, > > Reviewed-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx> Thanks, Leo
