06 Dec, 2015
1 commit
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For debugging low level code interacting with the CPU it is often
useful to trace the MSR read/writes. This gives a concise summary of
PMU and other operations.perf has an ad-hoc way to do this using trace_printk, but it's
somewhat limited (and also now spews ugly boot messages when enabled)Instead define real trace points for all MSR accesses.
This adds three new trace points: read_msr and write_msr and rdpmc.
They also report if the access faulted (if *_safe is used)
This allows filtering and triggering on specific MSR values, which
allows various more advanced debugging techniques.All the values are well defined in the CPU documentation.
The trace can be post processed with
Documentation/trace/postprocess/decode_msr.py to add symbolic MSR
names to the trace.I only added it to native MSR accesses in C, not paravirtualized or in
entry*.S (which is not too interesting)Originally the patch kit moved the MSRs out of line. This uses an
alternative approach recommended by Steven Rostedt of only moving the
trace calls out of line, but open coding the access to the jump label.Signed-off-by: Andi Kleen
Signed-off-by: Peter Zijlstra (Intel)
Acked-by: Steven Rostedt
Cc: Arnaldo Carvalho de Melo
Cc: Jiri Olsa
Cc: Linus Torvalds
Cc: Mike Galbraith
Cc: Peter Zijlstra
Cc: Stephane Eranian
Cc: Thomas Gleixner
Cc: Vince Weaver
Link: http://lkml.kernel.org/r/1449018060-1742-3-git-send-email-andi@firstfloor.org
Signed-off-by: Ingo Molnar
