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
-- 
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.

Reply via email to