On 27 January 2017 at 05:12, Alexander Shishkin <[email protected]> wrote: > Mathieu Poirier <[email protected]> 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.
Hence my statement about a change in behaviour. > 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. Specifying a size of zero with a range filter is wrong and as such should be treated as an error, which is what the current code is doing. If people want a start filter they can use the syntax required for that. In my opinion treating a range filter with a size zero as a start filter is adding intelligence to the machine, something that should probably be avoided. > >> 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. Then filter->action could be renamed 'type'. In the end filters on PT are range filters, the same way they are on CS. But changing the naming convention is a matter of personal opinion - I am fine with what we currently have. On the flip side reordering the fields in the 'if_tokens' match table would allow to set the filters properly in perf_event_parse_addr_filter(), keep the current behaviour intact and get rid of filter->range. Thanks, Mathieu > > Regards, > -- > Alex
