On Wed, Nov 06, 2019 at 01:01:41AM +0000, Ganapatrao Prabhakerrao Kulkarni wrote: > When perf tried with more events than the PMU supported counters, the perf > core uses event multiplexing to accommodate all events. This results in > burst of PMU register read and writes and causes the system hang, when > executed along with the CPU intensive applications. Can you please elaborate on how a burst of PMU reads/writes leads to a hang? I see the PMU counts DMC/L3C events -- does this occur under heavy /cpu/ load, or heavy /memory/ load? Does this only happen with a specific timing of reads/writes, or is it always possible that accessing the PMU can trigger a lockup, and it's just more likely when the PMU is accessed more often? Thanks, Mark. > > Adding software workaround by disabling event multiplexing. > > Signed-off-by: Ganapatrao Prabhakerrao Kulkarni <gkulkarni@xxxxxxxxxxx> > --- > Documentation/admin-guide/perf/thunderx2-pmu.rst | 9 +++++++++ > drivers/perf/thunderx2_pmu.c | 3 ++- > 2 files changed, 11 insertions(+), 1 deletion(-) > > diff --git a/Documentation/admin-guide/perf/thunderx2-pmu.rst b/Documentation/admin-guide/perf/thunderx2-pmu.rst > index 08e33675853a..fff65382c887 100644 > --- a/Documentation/admin-guide/perf/thunderx2-pmu.rst > +++ b/Documentation/admin-guide/perf/thunderx2-pmu.rst > @@ -40,3 +40,12 @@ Examples:: > uncore_l3c_0/read_hit/,\ > uncore_l3c_0/inv_request/,\ > uncore_l3c_0/inv_hit/ sleep 1 > + > +ThunderX2 erratum 221: > +When perf tried with more events than the PMU supported counters, the perf core > +uses event multiplexing to accommodate all events. This results in burst of PMU > +registers read and write and leading to system hang when executed along with > +CPU intensive applications. > + > + > +Disabling PMUs event multiplexing capability. > diff --git a/drivers/perf/thunderx2_pmu.c b/drivers/perf/thunderx2_pmu.c > index 43d76c85da56..c443be8bd449 100644 > --- a/drivers/perf/thunderx2_pmu.c > +++ b/drivers/perf/thunderx2_pmu.c > @@ -563,7 +563,8 @@ static int tx2_uncore_pmu_register( > .start = tx2_uncore_event_start, > .stop = tx2_uncore_event_stop, > .read = tx2_uncore_event_read, > - .capabilities = PERF_PMU_CAP_NO_EXCLUDE, > + .capabilities = PERF_PMU_CAP_NO_EXCLUDE | > + PERF_PMU_CAP_NO_MUX_EVENTS, > }; > > tx2_pmu->pmu.name = devm_kasprintf(dev, GFP_KERNEL, > -- > 2.17.1 >
