linux-kernel - Re: [PATCH v4 2/6] perf: hisi: Add support for HiSilicon SoC uncore PMU driver

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Message-ID: <20170815101627.GC6090@leverpostej>
Date:   Tue, 15 Aug 2017 11:16:27 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Shaokun Zhang <zhangshaokun@...ilicon.com>
Cc:     will.deacon@....com, jonathan.cameron@...wei.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linuxarm@...wei.com
Subject: Re: [PATCH v4 2/6] perf: hisi: Add support for HiSilicon SoC uncore
 PMU driver

Hi,

On Tue, Jul 25, 2017 at 08:10:38PM +0800, Shaokun Zhang wrote:
> +/* Read Super CPU cluster and CPU cluster ID from MPIDR_EL1 */
> +void hisi_read_sccl_and_ccl_id(u32 *sccl_id, u32 *ccl_id)
> +{
> +	u64 mpidr;
> +
> +	mpidr = read_cpuid_mpidr();
> +	if (mpidr & MPIDR_MT_BITMASK) {
> +		if (sccl_id)
> +			*sccl_id = MPIDR_AFFINITY_LEVEL(mpidr, 3);
> +		if (ccl_id)
> +			*ccl_id = MPIDR_AFFINITY_LEVEL(mpidr, 2);
> +	} else {
> +		if (sccl_id)
> +			*sccl_id = MPIDR_AFFINITY_LEVEL(mpidr, 2);
> +		if (ccl_id)
> +			*ccl_id = MPIDR_AFFINITY_LEVEL(mpidr, 1);
> +	}
> +}

How exactly are SCCLs organised w.r.t. MPIDRS?

Is this guaranteed to be correct for future SoCs?

It would be nicer if this were described explicitly by FW rather than
guessed at based on the MPIDR.

> +static bool hisi_validate_event_group(struct perf_event *event)
> +{
> +	struct perf_event *sibling, *leader = event->group_leader;
> +	struct hisi_pmu *hisi_pmu = to_hisi_pmu(event->pmu);
> +	/* Include count for the event */
> +	int counters = 1;
> +
> +	/*
> +	 * We must NOT create groups containing mixed PMUs, although
> +	 * software events are acceptable
> +	 */
> +	if (leader->pmu != event->pmu && !is_software_event(leader))
> +		return false;
> +
> +	/* Increment counter for the leader */
> +	counters++;

If this event is the leader, you account for it twice.

I guess you get away with that assuming you have at least two counters,
but it's less than ideal.

> +
> +	list_for_each_entry(sibling, &event->group_leader->sibling_list,
> +			    group_entry) {
> +		if (is_software_event(sibling))
> +			continue;
> +		if (sibling->pmu != event->pmu)
> +			return false;
> +		/* Increment counter for each sibling */
> +		counters++;
> +	}
> +
> +	/* The group can not count events more than the counters in the HW */
> +	return counters <= hisi_pmu->num_counters;
> +}

[...]

> +/*
> + * Set the counter to count the event that we're interested in,
> + * and enable counter and interrupt.
> + */
> +static void hisi_uncore_pmu_enable_event(struct perf_event *event)
> +{
> +	struct hisi_pmu *hisi_pmu = to_hisi_pmu(event->pmu);
> +	struct hw_perf_event *hwc = &event->hw;
> +
> +	/*
> +	 * Write event code in event select registers(for DDRC PMU,
> +	 * event has been mapped to fixed-purpose counter, there is
> +	 * no need to write event type).
> +	 */
> +	if (hisi_pmu->ops->write_evtype)
> +		hisi_pmu->ops->write_evtype(hisi_pmu, hwc->idx,
> +					    HISI_GET_EVENTID(event));

It looks like this is the only op which might be NULL. It would be
cleaner for the DDRC PMU code to provide an empty callback.

[...]

> +struct hisi_pmu *hisi_pmu_alloc(struct device *dev, u32 num_cntrs)
> +{
> +	struct hisi_pmu *hisi_pmu;
> +	struct hisi_pmu_hwevents *pmu_events;
> +
> +	hisi_pmu = devm_kzalloc(dev, sizeof(*hisi_pmu), GFP_KERNEL);
> +	if (!hisi_pmu)
> +		return ERR_PTR(-ENOMEM);
> +
> +	pmu_events = &hisi_pmu->pmu_events;
> +	pmu_events->hw_events = devm_kcalloc(dev,
> +					     num_cntrs,
> +					     sizeof(*pmu_events->hw_events),
> +					     GFP_KERNEL);
> +	if (!pmu_events->hw_events)
> +		return ERR_PTR(-ENOMEM);
> +
> +	pmu_events->used_mask = devm_kcalloc(dev,
> +					     BITS_TO_LONGS(num_cntrs),
> +					     sizeof(*pmu_events->used_mask),
> +					     GFP_KERNEL);

How big can num_counters be?

Assuming it's not too big, it would be nicer to embed these within the
hisi_pmu_hwevents.

[...]

> +
> +/* Generic pmu struct for different pmu types */
> +struct hisi_pmu {
> +	const char *name;
> +	struct pmu pmu;

struct pmu has a name field. Why do we need another?

> +	union {
> +		u32 ddrc_chn_id;
> +		u32 l3c_tag_id;
> +		u32 hha_uid;
> +	};

This would be simpler as a `u32 id` rather than a union.

> +	int num_counters;
> +	int num_events;

Subsequent patches intialise num_events, but it is never used. Was it
supposed to be checked at event_init time? Or is it unnnecessary?

Thanks,
Mark.