Messages in this thread | | | Date | Tue, 10 Jan 2017 16:04:19 -0600 | From | Kim Phillips <> | Subject | Re: [RFC PATCH 09/10] drivers/perf: Add support for ARMv8.2 Statistical Profiling Extension |
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On Tue, 3 Jan 2017 18:10:26 +0000 Will Deacon <will.deacon@arm.com> wrote:
> +#define DRVNAME "arm_spe_pmu"
Based on Intel naming "intel_pt" and "intel_bts', I had expected "arm-spe" as the universal basename for SPE. I don't really care about whether '_pmu' is included, but it's yet another naming inconsistency we have with coresight's "cs_etm" (the other being prefixed with "arm_").
Also, nit, since I don't know why perf userspace tools can't handle dashes in PMU names (commit 3d1ff755e367 "arm: perf: clean up PMU names" doesn't say), can we at least start to use dashes in our filenames? arm-spe-pmu.c is easier to type than arm_spe_pmu.c.
> +static int arm_spe_pmu_event_init(struct perf_event *event) > +{ > + u64 reg; > + struct perf_event_attr *attr = &event->attr; > + struct arm_spe_pmu *spe_pmu = to_spe_pmu(event->pmu); > + > + /* This is, of course, deeply driver-specific */ > + if (attr->type != event->pmu->type) > + return -ENOENT; > + > + if (event->cpu >= 0 && > + !cpumask_test_cpu(event->cpu, &spe_pmu->supported_cpus)) > + return -ENOENT; > + > + if (arm_spe_event_to_pmsevfr(event) & PMSEVFR_EL1_RES0) > + return -EOPNOTSUPP; > + > + if (event->hw.sample_period < spe_pmu->min_period || > + event->hw.sample_period & PMSIRR_EL1_IVAL_MASK) > + return -EOPNOTSUPP; > + > + if (attr->exclude_idle) > + return -EOPNOTSUPP; > + > + /* > + * Feedback-directed frequency throttling doesn't work when we > + * have a buffer of samples. We'd need to manually count the > + * samples in the buffer when it fills up and adjust the event > + * count to reflect that. Instead, force the user to specify a > + * sample period instead. > + */ > + if (attr->freq) > + return -EINVAL; > + > + if (is_kernel_in_hyp_mode()) { > + if (attr->exclude_kernel != attr->exclude_hv) > + return -EOPNOTSUPP; > + } else if (!attr->exclude_hv) { > + return -EOPNOTSUPP; > + } > + > + reg = arm_spe_event_to_pmsfcr(event); > + if ((reg & BIT(PMSFCR_EL1_FE_SHIFT)) && > + !(spe_pmu->features & SPE_PMU_FEAT_FILT_EVT)) > + return -EOPNOTSUPP; > + > + if ((reg & BIT(PMSFCR_EL1_FT_SHIFT)) && > + !(spe_pmu->features & SPE_PMU_FEAT_FILT_TYP)) > + return -EOPNOTSUPP; > + > + if ((reg & BIT(PMSFCR_EL1_FL_SHIFT)) && > + !(spe_pmu->features & SPE_PMU_FEAT_FILT_LAT)) > + return -EOPNOTSUPP; > + > + return 0; > +}
Without being provided instructions on how to use, I had to add debug printks here to find out e.g., an event period *must* be specified with record -c, and then again to find out that only a certain set of numbers is allowed by the h/w (256, 512, etc.). Is it possible to report why the driver is returning an error before it does? Otherwise, all the user sees is, e.g.:
Error: The sys_perf_event_open() syscall returned with 19 (No such device) for event (arm_spe_pmu_0). /bin/dmesg may provide additional information. No CONFIG_PERF_EVENTS=y kernel support configured?
...and, in this case, with nothing in dmesg. And, IIRC, the above text is emitted only if perf is run with -v and/or built with DEBUG set. Granted, *that* problem is not explicitly relevant to this patch, but new drivers should nevertheless express their usage details better.
Also, curiously, arm_spe_pmu doesn't appear in 'perf list' (even when SPE h/w is present).
Other than that, this gets my:
Tested-by: Kim Phillips <kim.phillips@arm.com>
Thanks,
Kim
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