linux-kernel - Re: [PATCH v9 2/2] drivers/perf: hisi: Add driver for HiSilicon PCIe PMU

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Date:   Tue, 24 Aug 2021 15:31:38 +0100
From:   Will Deacon <will@...nel.org>
To:     Qi Liu <liuqi115@...wei.com>
Cc:     mark.rutland@....com, bhelgaas@...gle.com,
        linux-pci@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linuxarm@...wei.com,
        zhangshaokun@...ilicon.com
Subject: Re: [PATCH v9 2/2] drivers/perf: hisi: Add driver for HiSilicon PCIe
 PMU

Hi,

On Wed, Aug 18, 2021 at 01:12:46PM +0800, Qi Liu wrote:
> PCIe PMU Root Complex Integrated End Point(RCiEP) device is supported
> to sample bandwidth, latency, buffer occupation etc.
> 
> Each PMU RCiEP device monitors multiple Root Ports, and each RCiEP is
> registered as a PMU in /sys/bus/event_source/devices, so users can
> select target PMU, and use filter to do further sets.
> 
> Filtering options contains:
> event     - select the event.
> port      - select target Root Ports. Information of Root Ports are
>             shown under sysfs.
> bdf       - select requester_id of target EP device.
> trig_len  - set trigger condition for starting event statistics.
> trig_mode - set trigger mode. 0 means starting to statistic when bigger
>             than trigger condition, and 1 means smaller.
> thr_len   - set threshold for statistics.
> thr_mode  - set threshold mode. 0 means count when bigger than threshold,
>             and 1 means smaller.

I think this is getting there now, thanks for sticking with it. Just a
couple of comments below..

> +static bool hisi_pcie_pmu_validate_event_group(struct perf_event *event)
> +{
> +	struct perf_event *sibling, *leader = event->group_leader;
> +	int counters = 1;
> +
> +	if (!is_software_event(leader)) {
> +		if (leader->pmu != event->pmu)
> +			return false;
> +
> +		if (leader != event)
> +			counters++;
> +	}
> +
> +	for_each_sibling_event(sibling, event->group_leader) {
> +		if (is_software_event(sibling))
> +			continue;
> +
> +		if (sibling->pmu != event->pmu)
> +			return false;
> +
> +		counters++;
> +	}
> +
> +	return counters <= HISI_PCIE_MAX_COUNTERS;
> +}

Given that this function doesn't look at the event numbers, doesn't this
over-provision the counter registers? For example, if I create a group
containing 4 of the same event, then we'll allocate four counters but only
use one. Similarly, if I create a group containing two events, one for the
normal counter and one for the extended counter, then we'll again allocate
two counters instead of one.

Have I misunderstood?

> +static int hisi_pcie_pmu_event_init(struct perf_event *event)
> +{
> +	struct hisi_pcie_pmu *pcie_pmu = to_pcie_pmu(event->pmu);
> +	struct hw_perf_event *hwc = &event->hw;
> +
> +	event->cpu = pcie_pmu->on_cpu;
> +
> +	if (EXT_COUNTER_IS_USED(hisi_pcie_get_event(event)))
> +		hwc->event_base = HISI_PCIE_EXT_CNT;
> +	else
> +		hwc->event_base = HISI_PCIE_CNT;
> +
> +	if (event->attr.type != event->pmu->type)
> +		return -ENOENT;
> +
> +	/* Sampling is not supported. */
> +	if (is_sampling_event(event) || event->attach_state & PERF_ATTACH_TASK)
> +		return -EOPNOTSUPP;
> +
> +	if (!hisi_pcie_pmu_valid_filter(event, pcie_pmu)) {
> +		pci_err(pcie_pmu->pdev, "Invalid filter!\n");

Please remove this message, as it's triggerable from userspace.

Will