Re: [PATCH 1/3] perf, pt, coresight: Clean up address filter structure

[Alexander Shishkin <alexander.shishkin@linux.intel.com>]

Mathieu Poirier <mathieu.poirier@linaro.org> writes:

> Hi Alex,

Hi Mathieu,

> This changes the behavior we used to have.  Now a range filter with a size of 0
> will be treated as start filter rather than an error.  See below on a possible
> way of fixing this.

Not really. Currently we have 2 drivers using this and both reject the
type=range&&size==0 filters with either -EOPNOTSUPP or -EINVAL. With
this change, PT will still reject it as it doesn't support single
address triggers, but Coresight will treat it as if it was a single
address filter. Which makes sense, because that's what a range of size
zero is. Note, that a range that covers one instruction has to be at
least size==1 (and I'm guessing size==4 for Coresight, but I may be
wrong).

So yes, this does change the existing behavior, but in doing so it
removes the ambiguity of zero sized ranges.

>                         if (filter->action == PERF_ADDR_FILTER_ACTION_RANGE)

But "range" is not an action, it's a type of a filter. It determines the
condition that triggers an action. An action, however, is what we do
when the condition comes true.

Regards,
--
Alex