powerpc/perf: Don't use perf_hw_context for trace IMC PMU

Trace IMC (In-Memory collection counters) in powerpc is useful for
application level profiling.

For trace_imc, presently task context (task_ctx_nr) is set to
perf_hw_context. But perf_hw_context should only be used for CPU PMU.
See commit 45fe361e83dd ("perf/core: Verify we have a single
perf_hw_context PMU").

So for trace_imc, even though it is per thread PMU, it is preferred to
use sw_context in order to be able to do application level monitoring.
Hence change the task_ctx_nr to use perf_sw_context.

Fixes: 5861ecd6beb8 ("powerpc/perf: Trace imc PMU functions")
Signed-off-by: Athira Rajeev <atrajeev@linux.vnet.ibm.com>
Reviewed-by: Madhavan Srinivasan <maddy@linux.vnet.ibm.com>
[mpe: Update subject & incorporate notes into change log, reflow comment]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220202041837.65968-1-atrajeev@linux.vnet.ibm.com

diff --git a/arch/powerpc/perf/imc-pmu.c b/arch/powerpc/perf/imc-pmu.c
index e106909ff9c377e557a83bfc3e257b4e9a0224a1..e7583fbcc8fa12de877fcb0ce635392deefd5946 100644 (file)
--- a/arch/powerpc/perf/imc-pmu.c
+++ b/arch/powerpc/perf/imc-pmu.c
@@ -1457,7 +1457,11 @@ static int trace_imc_event_init(struct perf_event *event)
 
        event->hw.idx = -1;
 
-       event->pmu->task_ctx_nr = perf_hw_context;
+       /*
+        * There can only be a single PMU for perf_hw_context events which is assigned to
+        * core PMU. Hence use "perf_sw_context" for trace_imc.
+        */
+       event->pmu->task_ctx_nr = perf_sw_context;
        event->destroy = reset_global_refc;
        return 0;
 }