linux-kernel - Re: [PATCH v2 5/5] perf: arm_cspmu: ampere

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Date:   Fri, 2 Jun 2023 00:13:36 -0700 (PDT)
From:   Ilkka Koskinen <ilkka@...amperecomputing.com>
To:     Robin Murphy <robin.murphy@....com>
cc:     Ilkka Koskinen <ilkka@...amperecomputing.com>,
        Jonathan Corbet <corbet@....net>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Besar Wicaksono <bwicaksono@...dia.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 5/5] perf: arm_cspmu: ampere_cspmu: Add support for
 Ampere SoC PMU


Hi Robin,

On Thu, 1 Jun 2023, Robin Murphy wrote:
> On 2023-06-01 04:01, Ilkka Koskinen wrote:
> [...]
>> +static bool ampere_cspmu_validate_event(struct arm_cspmu *cspmu,
>> +					struct perf_event *new)
>> +{
>> +	struct perf_event *curr;
>> +	unsigned int idx;
>> +	u32 threshold = 0, rank = 0, bank = 0;
>> +
>> +	/* We compare the global filter settings to existing events */
>> +	idx = find_first_bit(cspmu->hw_events.used_ctrs,
>> +			     cspmu->cycle_counter_logical_idx);
>> +
>> +	/* This is the first event */
>> +	if (idx == cspmu->cycle_counter_logical_idx)
>> +		return true;
>> +
>> +	curr = cspmu->hw_events.events[idx];
>> +
>> +	if (get_filter_enable(new)) {
>> +		threshold	= get_threshold(new);
>> +		rank		= get_rank(new);
>> +		bank		= get_bank(new);
>> +	}
>> +
>> +	if (get_filter_enable(new) != get_filter_enable(curr) ||
>
> Is there any useful purpose in allowing the user to specify nonzero rank, 
> bank or threshold values with filter_enable=0? Assuming not, then between 
> this and ampere_cspmu_set_ev_filter() it appears that you don't need 
> filter_enable at all.

Not really. I dropped filter_enable at one point but restored it later to 
match the smmuv3 pmu driver. I totally agree, it's unnecessary and it's 
better to remove it completely.

Cheers, Ilkka

>
> Thanks,
> Robin.
>
>> +	    get_threshold(curr) != threshold ||
>> +	    get_rank(curr) != rank ||
>> +	    get_bank(curr) != bank)
>> +		return false;
>> +
>> +	return true;
>> +}
>