linux-kernel - Re: [PATCH v2 5/5] arm64: perf: Add support for chaining event counters

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Date:   Mon, 11 Jun 2018 14:54:16 +0100
From:   Suzuki K Poulose <Suzuki.Poulose@....com>
To:     Mark Rutland <mark.rutland@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        will.deacon@....com, robin.murphy@....com
Subject: Re: [PATCH v2 5/5] arm64: perf: Add support for chaining event
 counters

On 08/06/18 15:46, Suzuki K Poulose wrote:
> Hi Mark,
> 
> On 06/06/2018 07:01 PM, Mark Rutland wrote:
>> On Tue, May 29, 2018 at 11:55:56AM +0100, Suzuki K Poulose wrote:

> 
>>> -        value |= 0xffffffff00000000ULL;
>>> +        if (!armv8pmu_event_is_64bit(event))
>>> +            value |= 0xffffffff00000000ULL;
>>>           write_sysreg(value, pmccntr_el0);
>>> -    } else if (armv8pmu_select_counter(idx) == idx)
>>> -        write_sysreg(value, pmxevcntr_el0);
>>> +    } else
>>> +        armv8pmu_write_hw_counter(event, value);
>>>   }
>>
>>> +static inline void armv8pmu_write_event_type(struct perf_event *event)
>>> +{
>>> +    struct hw_perf_event *hwc = &event->hw;
>>> +    int idx = hwc->idx;
>>> +
>>> +    /*
>>> +     * For chained events, write the the low counter event type
>>> +     * followed by the high counter. The high counter is programmed
>>> +     * with CHAIN event code with filters set to count at all ELs.
>>> +     */
>>> +    if (armv8pmu_event_is_chained(event)) {
>>> +        u32 chain_evt = ARMV8_PMUV3_PERFCTR_CHAIN |
>>> +                ARMV8_PMU_INCLUDE_EL2;
>>> +
>>> +        armv8pmu_write_evtype(idx - 1, hwc->config_base);
>>> +        isb();
>>> +        armv8pmu_write_evtype(idx, chain_evt);
>>
>> The ISB isn't necessary here, AFAICT. We only do this while the PMU is
>> disabled; no?
> 
> You're right. I was just following the ARM ARM.

Taking another look, it is not clear about the semantics of "pmu->enable()"
and pmu->disable() callbacks. I don't see any reference to them in the perf core
driver anymore. The perf core uses add() / del () instead, with the PMU
turned off. Do you have any idea about the enable()/disable() callbacks ?
Am I missing something ?

Suzuki