Messages in this thread | | | Date | Tue, 13 Jan 2015 08:56:39 -0300 | From | Arnaldo Carvalho de Melo <> | Subject | Re: perf: PERF_FLAG_FD_OUTPUT has been broken since 2.6.35 |
| |
Em Tue, Jan 13, 2015 at 10:36:03AM +0100, Peter Zijlstra escreveu: > 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.
That is exactly my thinking, the world goes on while we set up perf to observe it :-)
- Arnaldo
| |