Messages in this thread | | | Date | Thu, 22 Feb 2018 12:38:39 -0800 | From | Saravana Kannan <> | Subject | Re: [PATCH v11 8/8] perf: ARM DynamIQ Shared Unit PMU support |
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On 02/22/2018 03:33 AM, Mark Rutland wrote: > On Wed, Feb 21, 2018 at 06:32:46PM -0800, Saravana Kannan wrote: >> On 01/02/2018 03:25 AM, Suzuki K Poulose wrote: >>> +static int dsu_pmu_event_init(struct perf_event *event) >>> +{ >>> + struct dsu_pmu *dsu_pmu = to_dsu_pmu(event->pmu); >>> + >>> + if (event->attr.type != event->pmu->type) >>> + return -ENOENT; >> >> You are checking if the caller set the attr.type "correctly". > > This is necessary for the case where perf_init_event() falls back to > iterating over the list of PMUs, if event->attr.type wasn't found in the > idr. > > Without this, we'd erroneously check events intended for other PMUs. > So this is correct, and necessary.
Right, I'm aware of this. Which is why I also mentioned below that we can't just blindly delete this.
>>> +static int dsu_pmu_device_probe(struct platform_device *pdev) > >>> + rc = perf_pmu_register(&dsu_pmu->pmu, name, -1); >> >> You are passing in -1 here. Which means the event type is assigned by the >> perf framework. perf framework uses idr_alloc(&pmu_idr, ...) to get the id. >> So the id assigned is going to depend on the probe order among the different >> PMU drivers in the board/platform. So, this seems pretty random. > > The dynamic IDs are supposed to by looked up by name. > > Each PMU has a folder: /sys/bus/event_source/devices/$PMU > > ... with /sys/bus/event_source/devices/$PMU/type giving the type. > >> How is the caller supposed to know what to set the "type" to? > > The perf tools understand this already. If you do: > > perf stat -e $PMU/config=0xf00/ > > ... they will look up the type for that PMU and use it automatically. >
Ah, thanks! This finally explains how this is supposed to work from userspace.
>> You also can't just delete the check in dsu_pmu_event_init() because the >> event numbers you expose overlap with the per-CPU event numbers. > > The type check is necessary and cannot be deleted. It provides a > namespace for the event IDs.
Right. Which is my point too.
>> I'm not exactly sure if we can add entries to perf_type_id. If that's >> allowed maybe we need to add something line PERF_TYPE_DSU and use that? >> >> Or if that's not allowed then would it be better to offset the DSU PMU >> events by some number (say 0x1000) and then delete the event type check or >> pass PERF_TYPE_RAW to perf_pmu_register()? > > As above, neither of these should be necessary. >
For the userspace interface. How about the kernel interface though? perf_event_create_kernel_counter() takes attr.type as an input. But there's no way to look up the DSU PMU's "type".
Thanks, Saravana
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