Date: Wed, 19 Jul 2017 21:31:01 +0800
From: Jonathan Cameron <Jonathan.Cameron@huawei.com>
To: Jan Glauber <jglauber@cavium.com>
CC: Mark Rutland <mark.rutland@arm.com>, Will Deacon <will.deacon@arm.com>,
        <linux-kernel@vger.kernel.org>, <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH v7 1/3] perf: cavium: Support memory controller PMU
 counters
Message-ID: <20170719212722.000017e1@huawei.com>
In-Reply-To: <20170719120847.21183-2-jglauber@cavium.com>
References: <20170719120847.21183-1-jglauber@cavium.com>
        <20170719120847.21183-2-jglauber@cavium.com>
Organization: Huawei
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On Wed, 19 Jul 2017 14:08:45 +0200
Jan Glauber <jglauber@cavium.com> wrote:

> Add support for the PMU counters on Cavium SOC memory controllers.
> 
> This patch also adds generic functions to allow supporting more
> devices with PMU counters.
> 
> Properties of the LMC PMU counters:
> - not stoppable
> - fixed purpose
> - read-only
> - one PCI device per memory controller
> 
> Signed-off-by: Jan Glauber <jglauber@cavium.com>
Hi Jan,

A few little things I noticed whilst taking a quick look.

Jonathan
> ---
>  drivers/perf/Kconfig       |   8 +
>  drivers/perf/Makefile      |   1 +
>  drivers/perf/cavium_pmu.c  | 416 +++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/cpuhotplug.h |   1 +
>  4 files changed, 426 insertions(+)
>  create mode 100644 drivers/perf/cavium_pmu.c
<snip>
> +
> +/*
> + * The pmu events are independent from CPUs. Provide a cpumask
> + * nevertheless to prevent perf from adding the event per-cpu and just
> + * set the mask to one online CPU. Use the same cpumask for all "uncore"
> + * devices.
> + *
> + * There is a performance penalty for accessing a device from a CPU on
> + * another socket, but we do not care.
> + */
> +static int cvm_pmu_offline_cpu(unsigned int old_cpu, struct hlist_node *node)
> +{
> +	struct cvm_pmu_dev *pmu_dev;
> +	int new_cpu;
> +
> +	pmu_dev = hlist_entry_safe(node, struct cvm_pmu_dev, cpuhp_node);
> +	if (!cpumask_test_and_clear_cpu(old_cpu, &pmu_dev->active_mask))
> +		return 0;
> +
> +	new_cpu = cpumask_any_but(cpu_online_mask, old_cpu);
> +	if (new_cpu >= nr_cpu_ids)
> +		return 0;
Blank line.
> +	perf_pmu_migrate_context(&pmu_dev->pmu, old_cpu, new_cpu);
> +	cpumask_set_cpu(new_cpu, &pmu_dev->active_mask);
nitpick : blank line here would help readability.
> +	return 0;
> +}
> +
> +static ssize_t cvm_pmu_attr_show_cpumask(struct device *dev,
> +					 struct device_attribute *attr,
> +					 char *buf)
> +{
> +	struct pmu *pmu = dev_get_drvdata(dev);
> +	struct cvm_pmu_dev *pmu_dev = container_of(pmu, struct cvm_pmu_dev, pmu);
> +
> +	return cpumap_print_to_pagebuf(true, buf, &pmu_dev->active_mask);
> +}
> +
> +static DEVICE_ATTR(cpumask, S_IRUGO, cvm_pmu_attr_show_cpumask, NULL);
> +
> +static struct attribute *cvm_pmu_attrs[] = {
> +	&dev_attr_cpumask.attr,
> +	NULL,
> +};
> +
> +static struct attribute_group cvm_pmu_attr_group = {
> +	.attrs = cvm_pmu_attrs,
> +};
> +
> +/*
> + * LMC (memory controller) counters:
> + * - not stoppable, always on, read-only
> + * - one PCI device per memory controller
> + */
> +#define LMC_CONFIG_OFFSET		0x188
> +#define LMC_CONFIG_RESET_BIT		BIT(17)
> +
> +/* LMC events */
> +#define LMC_EVENT_IFB_CNT		0x1d0
> +#define LMC_EVENT_OPS_CNT		0x1d8
> +#define LMC_EVENT_DCLK_CNT		0x1e0
> +#define LMC_EVENT_BANK_CONFLICT1	0x360
> +#define LMC_EVENT_BANK_CONFLICT2	0x368
> +
> +#define CVM_PMU_LMC_EVENT_ATTR(_name, _id)						\
> +	&((struct perf_pmu_events_attr[]) {						\
> +		{									\
> +			__ATTR(_name, S_IRUGO, cvm_pmu_event_sysfs_show, NULL),		\
> +			_id,								\
> +			"lmc_event=" __stringify(_id),					\
> +		}									\
> +	})[0].attr.attr
> +
> +/* map counter numbers to register offsets */
> +static int lmc_events[] = {
> +	LMC_EVENT_IFB_CNT,
> +	LMC_EVENT_OPS_CNT,
> +	LMC_EVENT_DCLK_CNT,
> +	LMC_EVENT_BANK_CONFLICT1,
> +	LMC_EVENT_BANK_CONFLICT2,
> +};
> +
> +static int cvm_pmu_lmc_add(struct perf_event *event, int flags)
> +{
> +	struct hw_perf_event *hwc = &event->hw;
> +
> +	return cvm_pmu_add(event, flags, LMC_CONFIG_OFFSET,
> +			   lmc_events[hwc->config]);
> +}
> +
> +PMU_FORMAT_ATTR(lmc_event, "config:0-2");
> +
> +static struct attribute *cvm_pmu_lmc_format_attr[] = {
> +	&format_attr_lmc_event.attr,
> +	NULL,
> +};
> +
> +static struct attribute_group cvm_pmu_lmc_format_group = {
> +	.name = "format",
> +	.attrs = cvm_pmu_lmc_format_attr,
> +};
> +
> +static struct attribute *cvm_pmu_lmc_events_attr[] = {
> +	CVM_PMU_LMC_EVENT_ATTR(ifb_cnt,		0),
> +	CVM_PMU_LMC_EVENT_ATTR(ops_cnt,		1),
> +	CVM_PMU_LMC_EVENT_ATTR(dclk_cnt,	2),
> +	CVM_PMU_LMC_EVENT_ATTR(bank_conflict1,	3),
> +	CVM_PMU_LMC_EVENT_ATTR(bank_conflict2,	4),
> +	NULL,
> +};
> +
> +static struct attribute_group cvm_pmu_lmc_events_group = {
> +	.name = "events",
> +	.attrs = cvm_pmu_lmc_events_attr,
> +};
> +
> +static const struct attribute_group *cvm_pmu_lmc_attr_groups[] = {
> +	&cvm_pmu_attr_group,
> +	&cvm_pmu_lmc_format_group,
> +	&cvm_pmu_lmc_events_group,
> +	NULL,
> +};
> +
> +static bool cvm_pmu_lmc_event_valid(u64 config)
> +{
> +	return (config < ARRAY_SIZE(lmc_events));
> +}
> +
> +static int cvm_pmu_lmc_probe(struct pci_dev *pdev)
> +{
> +	struct cvm_pmu_dev *next, *lmc;
> +	int nr = 0, ret = -ENOMEM;
> +
> +	lmc = kzalloc(sizeof(*lmc), GFP_KERNEL);
> +	if (!lmc)
> +		goto fail_nomem;
cleaner to do a direct return here as nothing to unwind.
return -ENOMEM;
> +
> +	lmc->map = ioremap(pci_resource_start(pdev, 0),
> +			   pci_resource_len(pdev, 0));
Might be overly paranoid, but ioremap can return NULL,
so should really be checked.

> +	list_for_each_entry(next, &cvm_pmu_lmcs, entry)
> +		nr++;
> +	lmc->pmu_name = kasprintf(GFP_KERNEL, "lmc%d", nr);
Check for error on the allocation.
> +
> +	lmc->pdev = pdev;
> +	lmc->num_counters = ARRAY_SIZE(lmc_events);
> +	lmc->pmu = (struct pmu) {
> +		.task_ctx_nr    = perf_invalid_context,
> +		.event_init	= cvm_pmu_event_init,
> +		.add		= cvm_pmu_lmc_add,
> +		.del		= cvm_pmu_del,
> +		.start		= cvm_pmu_start,
> +		.stop		= cvm_pmu_stop,
> +		.read		= cvm_pmu_read,
> +		.attr_groups	= cvm_pmu_lmc_attr_groups,
> +	};
> +
> +	cpuhp_state_add_instance_nocalls(CPUHP_AP_PERF_ARM_CVM_ONLINE,
> +					 &lmc->cpuhp_node);
This function can fail by the look of it.  Should be checking it's
return value really.

> +
> +	/*
> +	 * perf PMU is CPU dependent so pick a random CPU and migrate away
> +	 * if it goes offline.
> +	 */
> +	cpumask_set_cpu(smp_processor_id(), &lmc->active_mask);
> +
> +	ret = perf_pmu_register(&lmc->pmu, lmc->pmu_name, -1);
> +	if (ret)
> +		goto fail_hp;
> +
> +	list_add(&lmc->entry, &cvm_pmu_lmcs);
> +
> +	lmc->event_valid = cvm_pmu_lmc_event_valid;
These last two elements rather look like they might cause a
potential race as the perf_pmu_register has made the counters
available.
> +	dev_info(&pdev->dev, "Enabled %s PMU with %d counters\n",
> +		 lmc->pmu_name, lmc->num_counters);
> +	return 0;
> +
> +fail_hp:
> +	kfree(lmc->pmu_name);
Convention is to unwind in the opposite order to the way things
were created / set up.  Becomes more relevant once you are
checking more error codes.
> +	cpuhp_state_remove_instance(CPUHP_AP_PERF_ARM_CVM_ONLINE,
> +				    &lmc->cpuhp_node);
> +	iounmap(lmc->map);
> +	kfree(lmc);
> +fail_nomem:
> +	return ret;
> +}
> +
> +static int __init cvm_pmu_init(void)
> +{
> +	unsigned long implementor = read_cpuid_implementor();
> +	unsigned int vendor_id = PCI_VENDOR_ID_CAVIUM;
> +	struct pci_dev *pdev = NULL;
> +	int rc;
> +
> +	if (implementor != ARM_CPU_IMP_CAVIUM)
> +		return -ENODEV;
> +
> +	INIT_LIST_HEAD(&cvm_pmu_lmcs);
> +
> +	rc = cpuhp_setup_state_multi(CPUHP_AP_PERF_ARM_CVM_ONLINE,
> +				     "perf/arm/cvm:online", NULL,
> +				     cvm_pmu_offline_cpu);
> +
> +	/* detect LMC devices */
> +	while ((pdev = pci_get_device(vendor_id, 0xa022, pdev))) {
> +		if (!pdev)
> +			break;
> +		rc = cvm_pmu_lmc_probe(pdev);
> +		if (rc)
> +			return rc;
> +	}
> +	return 0;
> +}
A comment perhaps explaining why this is a late_initcall?  What
dependency are we forcing to be true?
> +late_initcall(cvm_pmu_init);
> diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
> index b56573b..78ac3d2 100644
> --- a/include/linux/cpuhotplug.h
> +++ b/include/linux/cpuhotplug.h
> @@ -141,6 +141,7 @@ enum cpuhp_state {
>  	CPUHP_AP_PERF_ARM_QCOM_L3_ONLINE,
>  	CPUHP_AP_WORKQUEUE_ONLINE,
>  	CPUHP_AP_RCUTREE_ONLINE,
> +	CPUHP_AP_PERF_ARM_CVM_ONLINE,
>  	CPUHP_AP_ONLINE_DYN,
>  	CPUHP_AP_ONLINE_DYN_END		= CPUHP_AP_ONLINE_DYN + 30,
>  	CPUHP_AP_X86_HPET_ONLINE,