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References: <20180425090047.6485-1-ganapatrao.kulkarni@cavium.com>
 <20180425090047.6485-3-ganapatrao.kulkarni@cavium.com> <20180426105938.y6unpt36lisb7kbr@lakrids.cambridge.arm.com>
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From:   Ganapatrao Kulkarni <gklkml16@gmail.com>
Date:   Tue, 15 May 2018 16:03:19 +0530
Message-ID: <CAKTKpr61zBW_D6v_Ck1Lcp0NJ4wPFOpgbiM5aU_EtuiFU-qp4Q@mail.gmail.com>
Subject: Re: [PATCH v4 2/2] ThunderX2: Add Cavium ThunderX2 SoC UNCORE PMU driver
To:     Mark Rutland <mark.rutland@arm.com>
Cc:     Ganapatrao Kulkarni <ganapatrao.kulkarni@cavium.com>,
        linux-doc@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>,
        linux-arm-kernel@lists.infradead.org,
        Will Deacon <Will.Deacon@arm.com>, jnair@caviumnetworks.com,
        Robert Richter <Robert.Richter@cavium.com>,
        Vadim.Lomovtsev@cavium.com, Jan.Glauber@cavium.com
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Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Hi Mark,


On Sat, May 5, 2018 at 12:16 AM, Ganapatrao Kulkarni <gklkml16@gmail.com> wrote:
> Hi Mark,
>
> On Thu, Apr 26, 2018 at 4:29 PM, Mark Rutland <mark.rutland@arm.com> wrote:
>> 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?
>
> It has been suggested from hw team  to sample before  3 to 4 seconds.
>
>>
>> What's the maximum clock speed for the L3C and DMC?
>
> L3C at 1.5GHz and DMC at 1.2GHz
>>
>> 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...
>
> 2 seconds seems to be sufficient. So far testing looks good.
>
>>
>> [...]
>>
>>> +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?
>
> ok
>>
>>> +     int counter;
>>
>> AFAICT, this counter field is never used.
>
> hmm ok, will remove.
>>
>>> +     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;
>>
>
> thanks, will change as suggested.
>
>>> +     /* 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;
>
> ok
>>
>> [...]
>>
>>> +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.
>
> thanks, will add hotplug callbacks.
>>
>> At hotplug time, you'll need to update the management CPU, calling
>> perf_pmu_migrate_context() when it is offlined.
>
> ok
>>
>> [...]
>>
>>> +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.

without this locking, i am seeing "BUG: scheduling while atomic" when
i run perf with more events together than the maximum counters
supported

>
> thanks, it seems to be not required.
>>
>>> +
>>> +/*
>>> + * 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?
>
> separate interface for DMC and L3c.
> channels within DMC/L3C are muxed.
>
>>
>> ... 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.
>
> both are same, it is numa node id from ACPI/firmware.
>
>>
>> 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.
>
> IMO,  node id is sufficient.
>
>>
>> It would be vastly more sane for this to not be muxed at all. :/
>
> i am helpless due to crappy hw design!
>
>>
>>> + *   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?
>
> thanks, i will add.
>
>>
>> The muxing and SMC sound quite scary. :/
>
> i too agree!, however i have no other option since the muxing register
> is a secure register.
>>
>>> +
>>> +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.
>
> ok, will change
>>
>>> +}
>>> +
>>> +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?
>
> not used/reserved bits.
>
>>
>>> +
>>> +     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.
>
> ok
>>
>>> +}
>>> +
>>> +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.
>
> ok
>>
>>> +}
>>> +
>>> +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?
>
> 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?
>
> the offsets are at 0x640, 0x64c, 0x658, 0x664,
>>
>>> +     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.
>
> thanks.
>>
>>> +
>>> +     if (pmu_uncore->uncore_dev->select_channel)
>>> +             pmu_uncore->uncore_dev->select_channel(event);
>>
>> This should always be non-NULL, right?
>
> yes, unwanted check at the moment, will remove.
>
>>
>> [...]
>>
>>> +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.
>
> I think this check to avoid the grouping of  multiple hw PMUs ,
> however it is allowed to group sw events along with hw PMUs.
>
>>
>>> +
>>> +     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().
>
> thanks, unnecessary check!
>>
>>> +
>>> +     /* 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.
>
> ok, will add 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.
>
> sure
>>
>> I *think* that can be done in the pmu::pmu_enable() and
>> pmu::pmu_disable() callbacks.
>
> ok
>>
>> Are there control bits to enable/disable all counters, or can that only
>> be done through the event configuration registers?
>
> only through config register.
>>
>>> +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.
>
> ok.
>>
>> [...]
>>
>>> +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?
>
> name already has node id suffix.
>>
>> [...]
>>
>>> +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...
>
> sure, i will rewrite code to have timer per channel and all active
> counters are updated when timer fires.
>
>>
>>> +
>>> +     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.
>
> ok
>>
>> [...]
>>
>>> +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.
>
> ok
>>
>> [...]
>>
>>> +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.
>
> ok.
>>
>> Which FW supports this interface?
>
> it is through vendor specific ATF runtime services.
>>
>> Thanks,
>> Mark.
>
> thanks,
> Ganapat

thanks
Ganapat