[PATCH v1 2/4] powerpc/64s/perf: add power_pmu_running to query whether perf is being used

[Athira Rajeev]

> On 18-Aug-2021, at 5:11 PM, Nicholas Piggin <npiggin at gmail.com> wrote:
> 
> Excerpts from Madhavan Srinivasan's message of August 17, 2021 11:06 pm:
>> 
>> On 8/16/21 12:59 PM, Nicholas Piggin wrote:
>>> Interrupt handling code would like to know whether perf is enabled, to
>>> know whether it should enable MSR[EE] to improve PMI coverage.
>>> 
>>> Cc: Madhavan Srinivasan <maddy at linux.ibm.com>
>>> Cc: Athira Rajeev <atrajeev at linux.vnet.ibm.com>
>>> Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
>>> ---
>>>  arch/powerpc/include/asm/hw_irq.h |  2 ++
>>>  arch/powerpc/perf/core-book3s.c   | 13 +++++++++++++
>>>  2 files changed, 15 insertions(+)
>>> 
>>> diff --git a/arch/powerpc/include/asm/hw_irq.h b/arch/powerpc/include/asm/hw_irq.h
>>> index 21cc571ea9c2..2d5c0d3ccbb6 100644
>>> --- a/arch/powerpc/include/asm/hw_irq.h
>>> +++ b/arch/powerpc/include/asm/hw_irq.h
>>> @@ -306,6 +306,8 @@ static inline bool lazy_irq_pending_nocheck(void)
>>>  	return __lazy_irq_pending(local_paca->irq_happened);
>>>  }
>>> 
>>> +bool power_pmu_running(void);
>>> +
>>>  /*
>>>   * This is called by asynchronous interrupts to conditionally
>>>   * re-enable hard interrupts after having cleared the source
>>> diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
>>> index bb0ee716de91..76114a9afb2b 100644
>>> --- a/arch/powerpc/perf/core-book3s.c
>>> +++ b/arch/powerpc/perf/core-book3s.c
>>> @@ -2380,6 +2380,19 @@ static void perf_event_interrupt(struct pt_regs *regs)
>>>  	perf_sample_event_took(sched_clock() - start_clock);
>>>  }
>>> 
>>> +bool power_pmu_running(void)
>>> +{
>>> +	struct cpu_hw_events *cpuhw;
>>> +
>>> +	/* Could this simply test local_paca->pmcregs_in_use? */
>>> +
>>> +	if (!ppmu)
>>> +		return false;
>> 
>> 
>> This covers only when perf platform driver is not registered,
>> but we should also check for MMCR0[32], since pmu sprs can be
>> accessed via sysfs.
> 
> In that case do they actually do anything with the PMI? I don't think it 
> should matter hopefully.
> 
> But I do think a lot of this stuff could be cleaned up. We have 
> pmcs_enabled and ppc_enable_pmcs() in sysfs.c, ppc_set_pmu_inuse(), 
> ppc_md.enable_pmcs(), reserve_pmc_hardware(), etc and different users 
> call different things. We don't consistently disable either, e.g., we 
> never disable the H_PERFMON facility after we stop using perf even 
> though it says that slows down partition switch.

Hi Nick,

I have started looking at understanding the code path and working on it to get the code cleaned up.
I will work on posting the patch set for clean up.

Thanks
Athira Rajeev
> 
> I started to have a look at sorting it out but it looks like a big
> job so would take a bit of time if we want to do it.
> 
> Thanks,
> Nick