On 9/16/2016 12:40 PM, Mark Rutland wrote:
> On Fri, Sep 16, 2016 at 11:33:39AM -0400, Neil Leeder wrote:
[...]
>> On 9/1/2016 12:30 PM, Mark Rutland wrote:
>>> On Tue, Aug 30, 2016 at 01:01:33PM -0400, Neil Leeder wrote:
>>>> + /* Don't allow groups with mixed PMUs, except for s/w events */
>>>> + if (event->group_leader->pmu != event->pmu &&
>>>> + !is_software_event(event->group_leader)) {
>>>> + dev_warn(&l2cache_pmu->pdev->dev,
>>>> + "Can't create mixed PMU group\n");
>>>> + return -EINVAL;
>>>> + }
>>>> +
>>>> + list_for_each_entry(sibling, &event->group_leader->sibling_list,
>>>> + group_entry)
>>>> + if (sibling->pmu != event->pmu &&
>>>> + !is_software_event(sibling)) {
>>>> + dev_warn(&l2cache_pmu->pdev->dev,
>>>> + "Can't create mixed PMU group\n");
>>>> + return -EINVAL;
>>>> + }
>>>> +
>>>> + hwc->idx = -1;
>>>> + hwc->config_base = event->attr.config;
>>>> +
>>>> + /*
>>>> + * Ensure all events are on the same cpu so all events are in the
>>>> + * same cpu context, to avoid races on pmu_enable etc.
>>>> + */
>>>> + slice = get_hml2_pmu(event->cpu);
>>>> + event->cpu = slice->on_cpu;
>>>
>>> This could put an event on a different CPU to its group siblings, which
>>> is broken.
>>
>> This is the same logic as in arm-ccn.c:arm_ccn_pmu_event_init(), where there
>> is a single CPU designated as the CPU to be used for all events.
>>
>> All events for this slice are forced to slice->on_cpu which is the CPU
>> set in the cpumask for this slice.
>
> The CCN is a little different. For the CCN, a single CPU is designated
> to handle *all* events.
>
> For this driver, a CPU is designated per-slice, judging by the existence
> of hml2_pmu::on_cpu (unless that's superfluous). We've only verified
> that the events are all for this PMU, not the same slice, and thus each
> event->cpu may differ.
>
I see. So I can add a check that the group_leader event must be on the
same slice, and thus on the same CPU.
>> I'm not sure how this can put an event on a different CPU to its group
>> siblings?
>
> In practice today, we'll try to schedule the event on it's group
> leader's CPU, but accounting and subsequent manipulation could go wrong.
>
> Thanks,
> Mark.
>
Neil
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