On Mon, 7 Nov 2011, Pekka Enberg wrote: > I've never heard ABI incompatibility used as an argument for perf. Ingo?
Never overtly. They're too clever for that. In any case, as a primary developer of a library (PAPI) that uses the perf_events ABI I have to say that having perf in the kernel has been a *major* pain for us. Unlike the perf developers, we *do* have to maintain backwards compatability. And we have a lot of nasty code in PAPI to handle this. Entirely because the perf_events ABI is not stable. It's mostly stable, but there are enough regressions to be a pain. It's problem enough that there's no way to know what version of the perf_event abi you are running against and we have to guess based on kernel version. This gets "fun" because all of the vendors have backported seemingly random chunks of perf_event code to their older kernels. And it often does seem as the perf developers don't care when something breaks in perf_events if it doesn't affect perf users. For example, the new NMI watchdog severely breaks perf_event event allocation if you are using FORMAT_GROUP. perf doesn't use this though, so none of the kernel developers seem to care. And unless I can quickly come up with a patch as an outsider, a few kernel versions will go by and the kernel devs will declare "well it was broken so long, now we don't have to fix it". Fun. Vince
