On Wed, Sep 10, 2025 at 02:58:05PM -0700, Ian Rogers wrote: > On Wed, Sep 10, 2025 at 1:10 PM Namhyung Kim <namhyung@xxxxxxxxxx> wrote: > > A nit. Can we have one actual event and an alias of it? > > > > I think 'branch-instructions' will be the actual event and 'branches' > > will be the alias. Then the description will be like > > > > branch-instructions > > [Retired branch instructions. Unit: cpu_atom] > > ... > > > > branches > > [This event is an alias of branch-instructions.] > > > > The same goes to 'cycles' and 'cpu-cycles'. > > Similar 'cs' and 'context-switches' in > tools/perf/pmu-events/arch/common/common/software.json. > > So there are a few different ways to do this: > > 1) In perf list detect two events have the same encoding and list them together. > 2) In the json have a new aliases list then either: > 2.1) gets expanded in jevents.py as part of the build, > 2.2) passes into the pmu-events.c and the C code is updated to use an > alias list associated with each event. > > Option (1) will have something like quadratic complexity, but a fast > perf list isn't a particular goal I've heard of. > Option (2.2) will mean the existing binary searches for events will > become a binary search for an event and then linear searches through > the aliases. To make this not a slowdown we'd likely need more lookup > tables to avoid the linear searches. > Option (2.1) feels the most plausible. I was hoping the json and the > sysfs layout would kind of match, this would be true after the > jevents.py expands the aliases. This option is already kind of already > done in the legacy cache case as the > tools/perf/pmu-events/make_legacy_cache.py is making this. We'd still > need option (1) with this. > > Anyway, I'm not sure these downsides are countered by a slightly > smaller hardware.json and software.json, or maybe we should just go > with option 1 if the perf list output is all you care about. Let me > know if you see a different way of making it happen. I don't think the > vendors will be particularly happy for their upstream formats to > change given other tools will rely on them. Well, I was asking just to update the description in JSON. I'm not sure if it's a common problem we need to solve. Updating a few known aliases in the hardware and software description would be fine. Thanks, Namhyung
