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SubjectRe: [PATCH v4 2/2] ThunderX2: Add Cavium ThunderX2 SoC UNCORE PMU driver
Hi,

On Wed, Apr 25, 2018 at 02:30:47PM +0530, Ganapatrao Kulkarni wrote:
> +
> +/* L3c and DMC has 16 and 8 channels per socket respectively.
> + * Each Channel supports UNCORE PMU device and consists of
> + * 4 independent programmable counters. Counters are 32 bit
> + * and does not support overflow interrupt, they needs to be
> + * sampled before overflow(i.e, at every 2 seconds).
> + */
> +
> +#define UNCORE_MAX_COUNTERS 4
> +#define UNCORE_L3_MAX_TILES 16
> +#define UNCORE_DMC_MAX_CHANNELS 8
> +
> +#define UNCORE_HRTIMER_INTERVAL (2 * NSEC_PER_SEC)

How was a period of two seconds chosen?

What's the maximum clock speed for the L3C and DMC?

Given that all channels compete for access to the muxed register
interface, I suspect we need to try more often than once every 2
seconds...

[...]

> +struct active_timer {
> + struct perf_event *event;
> + struct hrtimer hrtimer;
> +};
> +
> +/*
> + * pmu on each socket has 2 uncore devices(dmc and l3),
> + * each uncore device has up to 16 channels, each channel can sample
> + * events independently with counters up to 4.
> + *
> + * struct thunderx2_pmu_uncore_channel created per channel.
> + * struct thunderx2_pmu_uncore_dev per uncore device.
> + */
> +struct thunderx2_pmu_uncore_channel {
> + struct thunderx2_pmu_uncore_dev *uncore_dev;
> + struct pmu pmu;

Can we put the pmu first in the struct, please?

> + int counter;

AFAICT, this counter field is never used.

> + int channel;
> + DECLARE_BITMAP(counter_mask, UNCORE_MAX_COUNTERS);
> + struct active_timer *active_timers;

You should only need a single timer per channel, rather than one per
event.

I think you can get rid of the active_timer structure, and have:

struct perf_event *events[UNCORE_MAX_COUNTERS];
struct hrtimer timer;

> + /* to sync counter alloc/release */
> + raw_spinlock_t lock;
> +};
> +
> +struct thunderx2_pmu_uncore_dev {
> + char *name;
> + struct device *dev;
> + enum thunderx2_uncore_type type;
> + unsigned long base;

This should be:

void __iomem *base;

[...]

> +static ssize_t cpumask_show(struct device *dev,
> + struct device_attribute *attr, char *buf)
> +{
> + struct cpumask cpu_mask;
> + struct thunderx2_pmu_uncore_channel *pmu_uncore =
> + pmu_to_thunderx2_pmu_uncore(dev_get_drvdata(dev));
> +
> + /* Pick first online cpu from the node */
> + cpumask_clear(&cpu_mask);
> + cpumask_set_cpu(cpumask_first(
> + cpumask_of_node(pmu_uncore->uncore_dev->node)),
> + &cpu_mask);
> +
> + return cpumap_print_to_pagebuf(true, buf, &cpu_mask);
> +}

AFAICT cpumask_of_node() returns a mask that can include offline CPUs.

Regardless, I don't think that you can keep track of the management CPU
this way. Please keep track of the CPU the PMU should be managed by,
either with a cpumask or int embedded within the PMU structure.

At hotplug time, you'll need to update the management CPU, calling
perf_pmu_migrate_context() when it is offlined.

[...]

> +static int alloc_counter(struct thunderx2_pmu_uncore_channel *pmu_uncore)
> +{
> + int counter;
> +
> + raw_spin_lock(&pmu_uncore->lock);
> + counter = find_first_zero_bit(pmu_uncore->counter_mask,
> + pmu_uncore->uncore_dev->max_counters);
> + if (counter == pmu_uncore->uncore_dev->max_counters) {
> + raw_spin_unlock(&pmu_uncore->lock);
> + return -ENOSPC;
> + }
> + set_bit(counter, pmu_uncore->counter_mask);
> + raw_spin_unlock(&pmu_uncore->lock);
> + return counter;
> +}
> +
> +static void free_counter(struct thunderx2_pmu_uncore_channel *pmu_uncore,
> + int counter)
> +{
> + raw_spin_lock(&pmu_uncore->lock);
> + clear_bit(counter, pmu_uncore->counter_mask);
> + raw_spin_unlock(&pmu_uncore->lock);
> +}

I don't believe that locking is required in either of these, as the perf
core serializes pmu::add() and pmu::del(), where these get called.

> +
> +/*
> + * DMC and L3 counter interface is muxed across all channels.
> + * hence we need to select the channel before accessing counter
> + * data/control registers.

Are there separate interfaces for all-dmc-channels and all-l3c-channels?

... or is a single interface used by all-dmc-and-l3c-channels?

> + *
> + * L3 Tile and DMC channel selection is through SMC call
> + * SMC call arguments,
> + * x0 = THUNDERX2_SMC_CALL_ID (Vendor SMC call Id)
> + * x1 = THUNDERX2_SMC_SET_CHANNEL (Id to set DMC/L3C channel)
> + * x2 = Node id

How do we map Linux node IDs to the firmware's view of node IDs?

I don't believe the two are necessarily the same -- Linux's node IDs are
a Linux-specific construct.

It would be much nicer if we could pass something based on the MPIDR,
which is a known HW construct, or if this implicitly affected the
current node.

It would be vastly more sane for this to not be muxed at all. :/

> + * x3 = DMC(1)/L3C(0)
> + * x4 = channel Id
> + */
> +static void uncore_select_channel(struct perf_event *event)
> +{
> + struct arm_smccc_res res;
> + struct thunderx2_pmu_uncore_channel *pmu_uncore =
> + pmu_to_thunderx2_pmu_uncore(event->pmu);
> +
> + arm_smccc_smc(THUNDERX2_SMC_CALL_ID, THUNDERX2_SMC_SET_CHANNEL,
> + pmu_uncore->uncore_dev->node,
> + pmu_uncore->uncore_dev->type,
> + pmu_uncore->channel, 0, 0, 0, &res);
> +
> +}

Why aren't we checking the return value of the SMC call?

The muxing and SMC sound quite scary. :/

> +
> +static void uncore_start_event_l3c(struct perf_event *event, int flags)
> +{
> + u32 val;
> + struct hw_perf_event *hwc = &event->hw;
> +
> + /* event id encoded in bits [07:03] */
> + val = GET_EVENTID(event) << 3;
> + reg_writel(val, hwc->config_base);
> +
> + if (flags & PERF_EF_RELOAD) {
> + u64 prev_raw_count =
> + local64_read(&event->hw.prev_count);
> + reg_writel(prev_raw_count, hwc->event_base);
> + }
> + local64_set(&event->hw.prev_count,
> + reg_readl(hwc->event_base));

It would be simpler to ignore PERF_EF_RELOAD, and always reprogram the
prev_count and HW to zero.

> +}
> +
> +static void uncore_start_event_dmc(struct perf_event *event, int flags)
> +{
> + u32 val, event_shift = 8;
> + struct hw_perf_event *hwc = &event->hw;
> +
> + /* enable and start counters and read current value in prev_count */
> + val = reg_readl(hwc->config_base);
> +
> + /* 8 bits for each counter,
> + * bits [05:01] of a counter to set event type.
> + */
> + reg_writel((val & ~(0x1f << (((GET_COUNTERID(event)) *
> + event_shift) + 1))) |
> + (GET_EVENTID(event) <<
> + (((GET_COUNTERID(event)) * event_shift) + 1)),
> + hwc->config_base);

This would be far more legible if val were constructed before the
reg_writel(), especially if there were a helper for the event field
shifting, e.g.

#define DMC_EVENT_CFG(idx, val) ((val) << (((idx) * 8) + 1))

int id = GET_COUNTERID(event);
int event = GET_EVENTID(event);

val = reg_readl(hwc->config_base);
val &= ~DMC_EVENT_CFG(id, 0x1f);
val |= DMCC_EVENT_CFG(id, event);
reg_writel(val, hwc->config_base));

What are bits 7:6 and 1 used for?

> +
> + if (flags & PERF_EF_RELOAD) {
> + u64 prev_raw_count =
> + local64_read(&event->hw.prev_count);
> + reg_writel(prev_raw_count, hwc->event_base);
> + }
> + local64_set(&event->hw.prev_count,
> + reg_readl(hwc->event_base));


As with the L3C events, it would be simpler to always reprogram the
prev_count and HW to zero.

> +}
> +
> +static void uncore_stop_event_l3c(struct perf_event *event)
> +{
> + reg_writel(0, event->hw.config_base);
> +}
> +
> +static void uncore_stop_event_dmc(struct perf_event *event)
> +{
> + u32 val, event_shift = 8;
> + struct hw_perf_event *hwc = &event->hw;
> +
> + val = reg_readl(hwc->config_base);
> + reg_writel((val & ~(0xff << ((GET_COUNTERID(event)) * event_shift))),
> + hwc->config_base);


This could be simplified with the helper proposed above.

> +}
> +
> +static void init_cntr_base_l3c(struct perf_event *event,
> + struct thunderx2_pmu_uncore_dev *uncore_dev)
> +{
> +
> + struct hw_perf_event *hwc = &event->hw;
> +
> + /* counter ctrl/data reg offset at 8 */

Offset 8, or stride 8?

What does the register layout look like?

> + hwc->config_base = uncore_dev->base
> + + L3C_COUNTER_CTL + (8 * GET_COUNTERID(event));
> + hwc->event_base = uncore_dev->base
> + + L3C_COUNTER_DATA + (8 * GET_COUNTERID(event));
> +}
> +
> +static void init_cntr_base_dmc(struct perf_event *event,
> + struct thunderx2_pmu_uncore_dev *uncore_dev)
> +{
> +
> + struct hw_perf_event *hwc = &event->hw;
> +
> + hwc->config_base = uncore_dev->base
> + + DMC_COUNTER_CTL;
> + /* counter data reg offset at 0xc */

A stride of 0xc seems unusual.

What does the register layout look like?

> + hwc->event_base = uncore_dev->base
> + + DMC_COUNTER_DATA + (0xc * GET_COUNTERID(event));
> +}
> +
> +static void thunderx2_uncore_update(struct perf_event *event)
> +{
> + s64 prev, new = 0;
> + u64 delta;
> + struct hw_perf_event *hwc = &event->hw;
> + struct thunderx2_pmu_uncore_channel *pmu_uncore;
> + enum thunderx2_uncore_type type;
> +
> + pmu_uncore = pmu_to_thunderx2_pmu_uncore(event->pmu);
> + type = pmu_uncore->uncore_dev->type;

AFAICT this variable is not used below.

> +
> + if (pmu_uncore->uncore_dev->select_channel)
> + pmu_uncore->uncore_dev->select_channel(event);

This should always be non-NULL, right?

[...]

> +static bool thunderx2_uncore_validate_event_group(struct perf_event *event)
> +{
> + struct pmu *pmu = event->pmu;
> + struct perf_event *leader = event->group_leader;
> + struct perf_event *sibling;
> + int counters = 0;
> +
> + if (leader->pmu != event->pmu && !is_software_event(leader))
> + return false;
> +
> + counters++;

I don't think this is right when event != leader and the leader is a SW
event. In that case, the leader doesn't take a HW counter.

> +
> + for_each_sibling_event(sibling, event->group_leader) {
> + if (is_software_event(sibling))
> + continue;
> + if (sibling->pmu != pmu)
> + return false;
> + counters++;
> + }
> +
> + /*
> + * If the group requires more counters than the HW has,
> + * it cannot ever be scheduled.
> + */
> + return counters <= UNCORE_MAX_COUNTERS;
> +}

[...]

> +static int thunderx2_uncore_event_init(struct perf_event *event)
> +{
> + struct hw_perf_event *hwc = &event->hw;
> + struct thunderx2_pmu_uncore_channel *pmu_uncore;

> + pmu_uncore = pmu_to_thunderx2_pmu_uncore(event->pmu);
> +
> + if (!pmu_uncore)
> + return -ENODEV;

This cannot happen, given pmu_to_thunderx2_pmu_uncore() is a wrapper
around container_of().

> +
> + /* Pick first online cpu from the node */
> + event->cpu = cpumask_first(
> + cpumask_of_node(pmu_uncore->uncore_dev->node));

I don't believe this is safe. You must keep track of which CPU is
managing the PMU, with hotplug callbacks.

[...]

> +static void thunderx2_uncore_start(struct perf_event *event, int flags)
> +{
> + struct hw_perf_event *hwc = &event->hw;
> + struct thunderx2_pmu_uncore_channel *pmu_uncore;
> + struct thunderx2_pmu_uncore_dev *uncore_dev;
> + unsigned long irqflags;
> + struct active_timer *active_timer;
> +
> + hwc->state = 0;
> + pmu_uncore = pmu_to_thunderx2_pmu_uncore(event->pmu);
> + uncore_dev = pmu_uncore->uncore_dev;
> +
> + raw_spin_lock_irqsave(&uncore_dev->lock, irqflags);
> +
> + if (uncore_dev->select_channel)
> + uncore_dev->select_channel(event);
> + uncore_dev->start_event(event, flags);
> + raw_spin_unlock_irqrestore(&uncore_dev->lock, irqflags);
> +
> + perf_event_update_userpage(event);
> + active_timer = &pmu_uncore->active_timers[GET_COUNTERID(event)];
> + active_timer->event = event;
> +
> + hrtimer_start(&active_timer->hrtimer,
> + ns_to_ktime(uncore_dev->hrtimer_interval),
> + HRTIMER_MODE_REL_PINNED);
> +}

Please use a single hrtimer, and update *all* of the events when it
fires.

I *think* that can be done in the pmu::pmu_enable() and
pmu::pmu_disable() callbacks.

Are there control bits to enable/disable all counters, or can that only
be done through the event configuration registers?

> +static void thunderx2_uncore_stop(struct perf_event *event, int flags)
> +{
> + struct hw_perf_event *hwc = &event->hw;
> + struct thunderx2_pmu_uncore_channel *pmu_uncore;
> + struct thunderx2_pmu_uncore_dev *uncore_dev;
> + unsigned long irqflags;
> +
> + if (hwc->state & PERF_HES_UPTODATE)
> + return;
> +
> + pmu_uncore = pmu_to_thunderx2_pmu_uncore(event->pmu);
> + uncore_dev = pmu_uncore->uncore_dev;
> +
> + raw_spin_lock_irqsave(&uncore_dev->lock, irqflags);
> +
> + if (uncore_dev->select_channel)
> + uncore_dev->select_channel(event);

AFAICT this cannot be NULL.

[...]

> +static int thunderx2_pmu_uncore_register(
> + struct thunderx2_pmu_uncore_channel *pmu_uncore)
> +{
> + struct device *dev = pmu_uncore->uncore_dev->dev;
> + char *name = pmu_uncore->uncore_dev->name;
> + int channel = pmu_uncore->channel;
> +
> + /* Perf event registration */
> + pmu_uncore->pmu = (struct pmu) {
> + .attr_groups = pmu_uncore->uncore_dev->attr_groups,
> + .task_ctx_nr = perf_invalid_context,
> + .event_init = thunderx2_uncore_event_init,
> + .add = thunderx2_uncore_add,
> + .del = thunderx2_uncore_del,
> + .start = thunderx2_uncore_start,
> + .stop = thunderx2_uncore_stop,
> + .read = thunderx2_uncore_read,
> + };
> +
> + pmu_uncore->pmu.name = devm_kasprintf(dev, GFP_KERNEL,
> + "%s_%d", name, channel);

Does the channel idx take the NUMA node into account?

[...]

> +static int thunderx2_pmu_uncore_add(struct thunderx2_pmu_uncore_dev *uncore_dev,
> + int channel)
> +{

> + /* we can run up to (max_counters * max_channels) events
> + * simultaneously, allocate hrtimers per channel.
> + */
> + pmu_uncore->active_timers = devm_kzalloc(uncore_dev->dev,
> + sizeof(struct active_timer) * uncore_dev->max_counters,
> + GFP_KERNEL);

Please just fold a single hrtimer into the thunderx2_pmu_uncore_channel
structure, and you can get rid of this allocation...

> +
> + for (counter = 0; counter < uncore_dev->max_counters; counter++) {
> + hrtimer_init(&pmu_uncore->active_timers[counter].hrtimer,
> + CLOCK_MONOTONIC,
> + HRTIMER_MODE_REL);
> + pmu_uncore->active_timers[counter].hrtimer.function =
> + thunderx2_uncore_hrtimer_callback;
> + }

... and simplify this initialization.

[...]

> +static struct thunderx2_pmu_uncore_dev *init_pmu_uncore_dev(
> + struct device *dev, acpi_handle handle,
> + struct acpi_device *adev, u32 type)
> +{
> + struct thunderx2_pmu_uncore_dev *uncore_dev;
> + unsigned long base;

> + base = (unsigned long)devm_ioremap_resource(dev, &res);
> + if (IS_ERR((void *)base)) {
> + dev_err(dev, "PMU type %d: Fail to map resource\n", type);
> + return NULL;
> + }

Please treat this as a void __iomem *base.

[...]

> +static int thunderx2_uncore_probe(struct platform_device *pdev)
> +{
> + struct device *dev = &pdev->dev;
> + struct arm_smccc_res res;
> +
> + set_dev_node(dev, acpi_get_node(ACPI_HANDLE(dev)));
> +
> + /* Make sure firmware supports DMC/L3C set channel smc call */
> + arm_smccc_smc(THUNDERX2_SMC_CALL_ID, THUNDERX2_SMC_SET_CHANNEL,
> + dev_to_node(dev), 0, 0, 0, 0, 0, &res);
> + if (res.a0) {
> + dev_err(dev, "No Firmware support for PMU UNCORE(%d)\n",
> + dev_to_node(dev));
> + return -ENODEV;
> + }

Please re-use the uncore_select_channel() wrapper rather than
open-coding this.

Which FW supports this interface?

Thanks,
Mark.

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