linux-kernel - Re: [PATCH v2 5/6] drivers/perf: Add support for ARMv8.2 Statistical Profiling Extension

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Message-Id: <20170406193307.e1046706e122d80c036ad1a9@arm.com>
Date:   Thu, 6 Apr 2017 19:33:07 +0100
From:   Kim Phillips <kim.phillips@....com>
To:     Will Deacon <will.deacon@....com>
Cc:     <linux-arm-kernel@...ts.infradead.org>, <marc.zyngier@....com>,
        <mark.rutland@....com>, <alex.bennee@...aro.org>,
        <christoffer.dall@...aro.org>, <tglx@...utronix.de>,
        <peterz@...radead.org>, <alexander.shishkin@...ux.intel.com>,
        <robh@...nel.org>, <suzuki.poulose@....com>, <pawel.moll@....com>,
        <mathieu.poirier@...aro.org>, <mingo@...hat.com>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 5/6] drivers/perf: Add support for ARMv8.2
 Statistical Profiling Extension

On Thu, 6 Apr 2017 17:18:15 +0100
Will Deacon <will.deacon@....com> wrote:

Hi Will,

> +/* Perf callbacks */
> +static int arm_spe_pmu_event_init(struct perf_event *event)
> +{
> +	u64 reg;
> +	struct perf_event_attr *attr = &event->attr;
> +	struct arm_spe_pmu *spe_pmu = to_spe_pmu(event->pmu);
> +
> +	/* This is, of course, deeply driver-specific */
> +	if (attr->type != event->pmu->type)
> +		return -ENOENT;
> +
> +	if (event->cpu >= 0 &&
> +	    !cpumask_test_cpu(event->cpu, &spe_pmu->supported_cpus))
> +		return -ENOENT;
> +
> +	if (arm_spe_event_to_pmsevfr(event) & PMSEVFR_EL1_RES0)
> +		return -EOPNOTSUPP;
> +
> +	if (event->hw.sample_period < spe_pmu->min_period ||
> +	    event->hw.sample_period & PMSIRR_EL1_IVAL_MASK)
> +		return -EOPNOTSUPP;
> +
> +	if (attr->exclude_idle)
> +		return -EOPNOTSUPP;
> +
> +	/*
> +	 * Feedback-directed frequency throttling doesn't work when we
> +	 * have a buffer of samples. We'd need to manually count the
> +	 * samples in the buffer when it fills up and adjust the event
> +	 * count to reflect that. Instead, force the user to specify a
> +	 * sample period instead.
> +	 */
> +	if (attr->freq)
> +		return -EINVAL;
> +
> +	if (is_kernel_in_hyp_mode()) {
> +		if (attr->exclude_kernel != attr->exclude_hv)
> +			return -EOPNOTSUPP;
> +	} else if (!attr->exclude_hv) {
> +		return -EOPNOTSUPP;
> +	}
> +
> +	reg = arm_spe_event_to_pmsfcr(event);
> +	if ((reg & BIT(PMSFCR_EL1_FE_SHIFT)) &&
> +	    !(spe_pmu->features & SPE_PMU_FEAT_FILT_EVT))
> +		return -EOPNOTSUPP;
> +
> +	if ((reg & BIT(PMSFCR_EL1_FT_SHIFT)) &&
> +	    !(spe_pmu->features & SPE_PMU_FEAT_FILT_TYP))
> +		return -EOPNOTSUPP;
> +
> +	if ((reg & BIT(PMSFCR_EL1_FL_SHIFT)) &&
> +	    !(spe_pmu->features & SPE_PMU_FEAT_FILT_LAT))
> +		return -EOPNOTSUPP;
> +
> +	return 0;
> +}

Can you please explain why we're not emitting messages to dmesg here?:

https://patchwork.kernel.org/patch/9545979/

I sure find them useful.

Thanks,

Kim