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SubjectRe: [PATCH 2/2] perf: add arm64 smmuv3 pmu driver
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Hi Robin,
Thank you for your comments.

On 8/7/2017 10:31 AM, Robin Murphy wrote:
> On 04/08/17 20:59, Neil Leeder wrote:
>> PMUs are named smmu_0_<phys_addr_page> where <phys_addr_page>
>> is the physical page address of the SMMU PMCG.
>> For example, the SMMU PMCG at 0xff88840000 is named smmu_0_ff88840
>
> This seems a bit rough - is it at feasible to at least chase the node
> reference and namespace them by the associated component, e.g. something
> like "arm-smmu-v3.x:pmcg.y"? The user can always dig the associated
> physical address out of /proc/iomem if necessary.
>
That looks like it may be better - I'll look into it.

>> Filtering by stream id is done by specifying filtering parameters
>> with the event. Options are:
>> filter_enable - 0 = no filtering, 1 = filtering enabled
>> filter_span - 0 = exact match, 1 = pattern match
>> filter_sec - applies to non-secure (0) or secure (1) namespace
>
> I'm a little dubious as to how useful it is to expose this, since we
> can't see the true value of SCR.SO so have no way of knowing what we'll
> actually end up counting.

I can remove the sec filter.

>> +config ARM_SMMUV3_PMU
>> + bool "ARM SMMUv3 PMU"
>> + depends on PERF_EVENTS && ARM64 && ACPI
>
> PERF_EVENTS is already a top-level dependency now.
>
OK

>> +#include <linux/msi.h>
>
> Is MSI support planned?
>
Not in this patchset. I'll remove the include.

>> +#define SMMU_PMCG_EVCNTR0 0x0
>> +#define SMMU_PMCG_EVCNTR(n, stride) (SMMU_PMCG_EVCNTR0 + (n) * (stride))
>> +#define SMMU_PMCG_EVTYPER0 0x400
>> +#define SMMU_PMCG_EVTYPER(n) (SMMU_PMCG_EVTYPER0 + (n) * 4)
>> +#define SMMU_PMCG_EVTYPER_SEC_SID_SHIFT 30
>> +#define SMMU_PMCG_EVTYPER_SID_SPAN_SHIFT 29
>> +#define SMMU_PMCG_EVTYPER_EVENT_MASK GENMASK(15, 0)
>> +#define SMMU_PMCG_SVR0 0x600
>> +#define SMMU_PMCG_SVR(n, stride) (SMMU_PMCG_SVR0 + (n) * (stride))
>> +#define SMMU_PMCG_SMR0 0xA00
>> +#define SMMU_PMCG_SMR(n) (SMMU_PMCG_SMR0 + (n) * 4)
>> +#define SMMU_PMCG_CNTENSET0 0xC00
>> +#define SMMU_PMCG_CNTENCLR0 0xC20
>> +#define SMMU_PMCG_INTENSET0 0xC40
>> +#define SMMU_PMCG_INTENCLR0 0xC60
>> +#define SMMU_PMCG_OVSCLR0 0xC80
>> +#define SMMU_PMCG_OVSSET0 0xCC0
>> +#define SMMU_PMCG_CAPR 0xD88
>> +#define SMMU_PMCG_SCR 0xDF8
>> +#define SMMU_PMCG_CFGR 0xE00
>> +#define SMMU_PMCG_CFGR_SID_FILTER_TYPE BIT(23)
>> +#define SMMU_PMCG_CFGR_CAPTURE BIT(22)
>> +#define SMMU_PMCG_CFGR_MSI BIT(21)
>> +#define SMMU_PMCG_CFGR_RELOC_CTRS BIT(20)
>> +#define SMMU_PMCG_CFGR_SIZE_MASK GENMASK(13, 8)
>> +#define SMMU_PMCG_CFGR_SIZE_SHIFT 8
>> +#define SMMU_PMCG_CFGR_COUNTER_SIZE_32 31
>> +#define SMMU_PMCG_CFGR_NCTR_MASK GENMASK(5, 0)
>> +#define SMMU_PMCG_CFGR_NCTR_SHIFT 0
>> +#define SMMU_PMCG_CR 0xE04
>> +#define SMMU_PMCG_CR_ENABLE BIT(0)
>> +#define SMMU_PMCG_CEID0 0xE20
>> +#define SMMU_PMCG_CEID1 0xE28
>> +#define SMMU_PMCG_IRQ_CTRL 0xE50
>> +#define SMMU_PMCG_IRQ_CTRL_IRQEN BIT(0)
>> +#define SMMU_PMCG_IRQ_CTRLACK 0xE54
>> +#define SMMU_PMCG_IRQ_CTRLACK_IRQEN BIT(0)
>> +#define SMMU_PMCG_IRQ_CFG0 0xE58
>> +#define SMMU_PMCG_IRQ_CFG0_ADDR_MASK GENMASK(51, 2)
>> +#define SMMU_PMCG_IRQ_CFG1 0xE60
>> +#define SMMU_PMCG_IRQ_CFG2 0xE64
>> +#define SMMU_PMCG_IRQ_STATUS 0xE68
>> +#define SMMU_PMCG_IRQ_STATUS_IRQ_ABT BIT(0)
>> +#define SMMU_PMCG_AIDR 0xE70
>
> Several of these are unused (although at least IRQ0_CFG1 probably should
> be, to zero it to a known state if we aren't supporting MSIs).
>
I can remove the unused defines and clear IRQ_CFG1.

>> + bool reg_size_32;
>
> This guy is redundant...
>
[...]
>> + if (smmu_pmu->reg_size_32)
>
> ...since it would be just as efficient to directly test
> smmu_pmu->counter_mask & BIT(32) here and below.
>
OK

>> +
>> + for (i = 0; i < smmu_pmu->num_counters; i++) {
>> + smmu_pmu_counter_disable(smmu_pmu, i);
>> + smmu_pmu_interrupt_disable(smmu_pmu, i);
>> + }
>
> Surely it would be far quicker and simpler to do this?
>
> writeq(smmu_pmu->counter_present_mask,
> smmu_pmu->reg_base + SMMU_PMCG_CNTENCLR0);
> writeq(smmu_pmu->counter_present_mask,
> smmu_pmu->reg_base + SMMU_PMCG_INTENCLR0);
>
OK

>> +static inline bool smmu_pmu_has_overflowed(struct smmu_pmu *smmu_pmu, u64 ovsr)
>> +{
>> + return !!(ovsr & smmu_pmu->counter_present_mask);
>> +}
>
> Personally, I find these helpers abstracting simple reads/writes
> actually make the code harder to follow, especially when they're each
> used a grand total of once. That may well just be me, though.
>
At least this one will go away with the below change to the interrupt handler.

>> + new = SMMU_COUNTER_RELOAD;
>
> Given that we *are* following the "use the top counter bit as an
> implicit overflow bit" pattern of arm_pmu, it feels a bit weird to not
> use the actual half-maximum value here (especially since it's easily
> computable from counter_mask). I'm about 85% sure it probably still
> works, but as ever inconsistency breeds uncertainty.

I thought that if we're happy with BIT(31) working fine with 32-bit registers,
it should also work for larger registers, so there was no need to waste more of
their bits. But I can change it to be half-max for all of them.

>> +static irqreturn_t smmu_pmu_handle_irq(int irq_num, void *data)
>> +{
>> + struct smmu_pmu *smmu_pmu = data;
>> + u64 ovsr;
>> + unsigned int idx;
>> +
>> + ovsr = smmu_pmu_getreset_ovsr(smmu_pmu);
>> + if (!smmu_pmu_has_overflowed(smmu_pmu, ovsr))
>
> You have an architectural guarantee that unimplemented bits of OVSSET0
> are RES0, so checking !ovsr is sufficient.
>
OK

>> + /* Verify specified event is supported on this PMU */
>> + event_id = get_event(event);
>> + if ((event_id >= SMMU_MAX_EVENT_ID) ||
>
> What about raw imp-def events?
>
I can keep the check for common events, but also allow any raw event
in the imp-def range.

>> + (!test_bit(event_id, smmu_pmu->supported_events))) {
>> + dev_dbg_ratelimited(&smmu_pmu->pdev->dev,
>> + "Invalid event %d for this PMU\n",
>> + event_id);
>> + return -EINVAL;
>> + }
[...]

>> +static int smmu_pmu_offline_cpu(unsigned int cpu, struct hlist_node *node)
>> +{
>> + struct smmu_pmu *smmu_pmu;
>> + unsigned int target;
>> +
>> + smmu_pmu = hlist_entry_safe(node, struct smmu_pmu, node);
>
> Is it ever valid for node to be NULL? If we can't trust it to be one of
> the PMUs we registered I think all bets are off anyway.
>
I was following the logic in arm-ccn.c and arm-cci.c. If it works for them
I would hope it works here too.

>> +
>> + ceid_64 = readq(smmu_pmu->reg_base + SMMU_PMCG_CEID0);
>> + ceid[0] = ceid_64 & GENMASK(31, 0);
>
> It took a second look to determine that that masking does nothing...
>
>> + ceid[1] = ceid_64 >> 32;
>> + ceid_64 = readq(smmu_pmu->reg_base + SMMU_PMCG_CEID1);
>> + ceid[2] = ceid_64 & GENMASK(31, 0);
>> + ceid[3] = ceid_64 >> 32;
>> + bitmap_from_u32array(smmu_pmu->supported_events, SMMU_MAX_EVENT_ID,
>> + ceid, SMMU_NUM_EVENTS_U32);
>
> ...but then the whole lot might be cleaner and simpler with a u64[2]
> cast to u32* (or unioned to u32[4]) as necessary.
>
I've rewritten this about 4 different ways and didn't love any of them,
including this one. I can re-do this as you suggest.

>> +static struct platform_driver smmu_pmu_driver = {
>> + .driver = {
>> + .name = "arm-smmu-pmu",
>
> Nit: "arm-smmu-v3-pmu" please, for consistency with the IOMMU driver
> naming. There is a SMMUv2 PMU driver in the works, too ;)
>
ok

Thanks,

Neil
--
Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project.

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