On 23 August 2016 at 11:02, Alexander Shishkin <[email protected]> wrote: > Mathieu Poirier <[email protected]> writes: > >> On 22 August 2016 at 09:15, Alexander Shishkin >> <[email protected]> wrote: >>> Mathieu Poirier <[email protected]> writes: >>> >>>> As such something that used to be a two-step process: >>>> >>>> # echo 1 > /sys/bus/coresight/devices/20070000.etr/enable_sink >>>> # perf record -e cs_etm//u --per-thread uname >>>> >>>> is integrated in a single command: >>>> >>>> # perf record -e cs_etm/@sink=20070000.etr/u --per-thread uname >>> >>> Can't we simply teach perf record to write 1 to that sysfs attribute and >>> avoid parsing more ascii strings in the kernel? I suspect that would also >>> take way less code. >> >> That, in my opinion, would be a big hack. Peter and Jiri, any thoughts on >> this? > > Why would you say it's a hack? The whole tracer->sink configuration is > outside of scope of perf framework, there is absolutely no reason why > perf core should do this, especially, add this to perf ABI.
That is why the solution was made generic - sink configuration is simply using it. > > It would have somewhat made sense if you could configure different > events on the same pmu to send data to different sinks, but even that > won't work, because you simply cannot guarantee sink's availability if > you have to release it when your event gets scheduled out. > >>> Are there any other use cases for this besides specifying @sink for a >>> ETM? >> >> Not at this time but there is so many configuration option for the >> ETM/PTM tracers (that aren't filters) that I wanted the right >> infrastructure to be there should/when we need to expand. > > As I've asked before, what exactly is the need for expansion? That is, > something more than purely hypothetical that needs to be configured in > the tracer, on per event basis, *and* does not fit into the event > attribute. Note that the sink configuration also doesn't fit the bill. The first thing that comes to mind is counters and state machine, something that I simply don't see fitting into the event attributes. But those could also be set via sysFS - the end result is exactly the same. > > Regards, > -- > Alex
