From: Athira Rajeev atrajeev@linux.vnet.ibm.com
[ Upstream commit 890005a7d98f7452cfe86dcfb2aeeb7df01132ce ]
commit 2c9ac51b850d ("powerpc/perf: Fix PMU callbacks to clear pending PMI before resetting an overflown PMC") added a new function "pmi_irq_pending" in hw_irq.h. This function is to check if there is a PMI marked as pending in Paca (PACA_IRQ_PMI).This is used in power_pmu_disable in a WARN_ON. The intention here is to provide a warning if there is PMI pending, but no counter is found overflown.
During some of the perf runs, below warning is hit:
WARNING: CPU: 36 PID: 0 at arch/powerpc/perf/core-book3s.c:1332 power_pmu_disable+0x25c/0x2c0 Modules linked in: -----
NIP [c000000000141c3c] power_pmu_disable+0x25c/0x2c0 LR [c000000000141c8c] power_pmu_disable+0x2ac/0x2c0 Call Trace: [c000000baffcfb90] [c000000000141c8c] power_pmu_disable+0x2ac/0x2c0 (unreliable) [c000000baffcfc10] [c0000000003e2f8c] perf_pmu_disable+0x4c/0x60 [c000000baffcfc30] [c0000000003e3344] group_sched_out.part.124+0x44/0x100 [c000000baffcfc80] [c0000000003e353c] __perf_event_disable+0x13c/0x240 [c000000baffcfcd0] [c0000000003dd334] event_function+0xc4/0x140 [c000000baffcfd20] [c0000000003d855c] remote_function+0x7c/0xa0 [c000000baffcfd50] [c00000000026c394] flush_smp_call_function_queue+0xd4/0x300 [c000000baffcfde0] [c000000000065b24] smp_ipi_demux_relaxed+0xa4/0x100 [c000000baffcfe20] [c0000000000cb2b0] xive_muxed_ipi_action+0x20/0x40 [c000000baffcfe40] [c000000000207c3c] __handle_irq_event_percpu+0x8c/0x250 [c000000baffcfee0] [c000000000207e2c] handle_irq_event_percpu+0x2c/0xa0 [c000000baffcff10] [c000000000210a04] handle_percpu_irq+0x84/0xc0 [c000000baffcff40] [c000000000205f14] generic_handle_irq+0x54/0x80 [c000000baffcff60] [c000000000015740] __do_irq+0x90/0x1d0 [c000000baffcff90] [c000000000016990] __do_IRQ+0xc0/0x140 [c0000009732f3940] [c000000bafceaca8] 0xc000000bafceaca8 [c0000009732f39d0] [c000000000016b78] do_IRQ+0x168/0x1c0 [c0000009732f3a00] [c0000000000090c8] hardware_interrupt_common_virt+0x218/0x220
This means that there is no PMC overflown among the active events in the PMU, but there is a PMU pending in Paca. The function "any_pmc_overflown" checks the PMCs on active events in cpuhw->n_events. Code snippet:
<<>> if (any_pmc_overflown(cpuhw)) clear_pmi_irq_pending(); else WARN_ON(pmi_irq_pending()); <<>>
Here the PMC overflown is not from active event. Example: When we do perf record, default cycles and instructions will be running on PMC6 and PMC5 respectively. It could happen that overflowed event is currently not active and pending PMI is for the inactive event. Debug logs from trace_printk:
<<>> any_pmc_overflown: idx is 5: pmc value is 0xd9a power_pmu_disable: PMC1: 0x0, PMC2: 0x0, PMC3: 0x0, PMC4: 0x0, PMC5: 0xd9a, PMC6: 0x80002011 <<>>
Here active PMC (from idx) is PMC5 , but overflown PMC is PMC6(0x80002011). When we handle PMI interrupt for such cases, if the PMC overflown is from inactive event, it will be ignored. Reference commit: commit bc09c219b2e6 ("powerpc/perf: Fix finding overflowed PMC in interrupt")
Patch addresses two changes: 1) Fix 1 : Removal of warning ( WARN_ON(pmi_irq_pending()); ) We were printing warning if no PMC is found overflown among active PMU events, but PMI pending in PACA. But this could happen in cases where PMC overflown is not in active PMC. An inactive event could have caused the overflow. Hence the warning is not needed. To know pending PMI is from an inactive event, we need to loop through all PMC's which will cause more SPR reads via mfspr and increase in context switch. Also in existing function: perf_event_interrupt, already we ignore PMI's overflown when it is from an inactive PMC.
2) Fix 2: optimization in clearing pending PMI. Currently we check for any active PMC overflown before clearing PMI pending in Paca. This is causing additional SPR read also. From point 1, we know that if PMI pending in Paca from inactive cases, that is going to be ignored during replay. Hence if there is pending PMI in Paca, just clear it irrespective of PMC overflown or not.
In summary, remove the any_pmc_overflown check entirely in power_pmu_disable. ie If there is a pending PMI in Paca, clear it, since we are in pmu_disable. There could be cases where PMI is pending because of inactive PMC ( which later when replayed also will get ignored ), so WARN_ON could give false warning. Hence removing it.
Fixes: 2c9ac51b850d ("powerpc/perf: Fix PMU callbacks to clear pending PMI before resetting an overflown PMC") Signed-off-by: Athira Rajeev atrajeev@linux.vnet.ibm.com Signed-off-by: Michael Ellerman mpe@ellerman.id.au Link: https://lore.kernel.org/r/20220522142256.24699-1-atrajeev@linux.vnet.ibm.com Signed-off-by: Sasha Levin sashal@kernel.org --- arch/powerpc/perf/core-book3s.c | 35 ++++++++++++++------------------- 1 file changed, 15 insertions(+), 20 deletions(-)
diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c index e78de7050947..1078784b74c9 100644 --- a/arch/powerpc/perf/core-book3s.c +++ b/arch/powerpc/perf/core-book3s.c @@ -1320,27 +1320,22 @@ static void power_pmu_disable(struct pmu *pmu) * a PMI happens during interrupt replay and perf counter * values are cleared by PMU callbacks before replay. * - * If any PMC corresponding to the active PMU events are - * overflown, disable the interrupt by clearing the paca - * bit for PMI since we are disabling the PMU now. - * Otherwise provide a warning if there is PMI pending, but - * no counter is found overflown. + * Disable the interrupt by clearing the paca bit for PMI + * since we are disabling the PMU now. Otherwise provide a + * warning if there is PMI pending, but no counter is found + * overflown. + * + * Since power_pmu_disable runs under local_irq_save, it + * could happen that code hits a PMC overflow without PMI + * pending in paca. Hence only clear PMI pending if it was + * set. + * + * If a PMI is pending, then MSR[EE] must be disabled (because + * the masked PMI handler disabling EE). So it is safe to + * call clear_pmi_irq_pending(). */ - if (any_pmc_overflown(cpuhw)) { - /* - * Since power_pmu_disable runs under local_irq_save, it - * could happen that code hits a PMC overflow without PMI - * pending in paca. Hence only clear PMI pending if it was - * set. - * - * If a PMI is pending, then MSR[EE] must be disabled (because - * the masked PMI handler disabling EE). So it is safe to - * call clear_pmi_irq_pending(). - */ - if (pmi_irq_pending()) - clear_pmi_irq_pending(); - } else - WARN_ON(pmi_irq_pending()); + if (pmi_irq_pending()) + clear_pmi_irq_pending();
val = mmcra = cpuhw->mmcr.mmcra;