On 21-Oct-2021, at 10:47 PM, Nathan Lynch <nathanl@linux.ibm.com> wrote:

Athira Rajeev <atrajeev@linux.vnet.ibm.com> writes:
During Live Partition Migration = (LPM), it is observed that perf
counter values reports = zero post migration completion. However
'perf stat' with = workload continues to show counts post migration
since PMU = gets disabled/enabled during sched switches. But incase
of = system/cpu wide monitoring, zero counts were reported with 'perf
stat' after migration completion.

Example:
./perf stat -e r1001e -I 1000
          tim= e =             co= unts unit events
    1.001010437 =         22,137,414 =      r1001e
    2.002495447 =         15,455,821 =      r1001e
<<>> As = seen in next below logs, the counter values shows zero
       after migration is = completed.
<<>>
   86.142535370 =    129,392,333,440 =      r1001e
   87.144714617 =             &n= bsp;    0      r1001e
   88.146526636 =             &n= bsp;    0      r1001e
   89.148085029 =             &n= bsp;    0      r1001e

Confirmed in my environment:

   51.099987985 =            300,338 =      cache-misses
   52.101839374 =            296,586 =      cache-misses
   53.116089796 =            263,150 =      cache-misses
   54.117949249 =            232,290 =      cache-misses
   55.602029375 =     68,700,421,711 =      cache-misses
   56.610073969 =             &n= bsp;    0 =      cache-misses
   57.614732000 =             &n= bsp;    0 =      cache-misses

I wonder what it means that there is a very unlikely huge = value before
the counter = stops working -- I believe your example has this phenomenon
too.

diff = --git a/arch/powerpc/platforms/pseries/mobility.c = b/arch/powerpc/platforms/pseries/mobility.c
index = e83e089..ff7a77c 100644
--- = a/arch/powerpc/platforms/pseries/mobility.c
+++ = b/arch/powerpc/platforms/pseries/mobility.c
@@ -476,6 = +476,8 @@ static int do_join(void *arg)
retry:
= /* Must ensure MSR.EE off for H_JOIN. */
= hard_irq_disable();
+ /* Disable PMU before suspend = */
+ mobility_pmu_disable();
hvrc =3D = plpar_hcall_norets(H_JOIN);

switch = (hvrc) {
@@ -530,6 +532,8 @@ static int do_join(void = *arg)
* = reset the watchdog.
*/
= touch_nmi_watchdog();
+ /* Enable PMU after resuming = */
+ mobility_pmu_enable();
return = ret;
}

We should minimize calls into other subsystems from this = context (the
callback = function we've passed to stop_machine); it's fairly sensitive.
Can this be moved out to = pseries_migrate_partition() or similar?