On Fri, Jan 09, 2015 at 11:26:54AM -0500, Vince Weaver wrote: > > On Fri, 9 Jan 2015, Peter Zijlstra wrote: > > > So is this worth fixing seeing as apparently no one uses this feature? > > > > I think there's a fair argument for removing it, Ingo, Acme? > > could the functionality be replaced with a subsequent call to > ioctl(PERF_EVENT_IOC_SET_OUTPUT)
Yes. > Although I suppose there's a possibility for losing a small amount of data > or some other reason that PERF_FLAG_FD_OUTPUT was introduced in the first > place. That's a natural race without solution. That is, because there is no serialization between the sys_perf_event_open() and any possible acts of data generation, we can't even talk about loosing data. Even if it were all in a single syscall, there is no saying how long that syscall would take to complete -- imagine its stuck on memory allocation or whatnot. Similarly you could have issued the syscall a wee bit later or whatnot. > In addition, if we remove PERF_FLAG_FD_OUTPUT would there then be any > reason to keep PERF_FLAG_FD_NO_GROUP around? Good point, I think there was another potential user of that proposed recently, but I can't quite remember where or what. Let me try and go find that. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
