Messages in this thread | | | Date | Wed, 03 Apr 2013 10:29:34 -0700 | From | John Stultz <> | Subject | Re: [RFC] perf: need to expose sched_clock to correlate user samples with kernel samples |
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On 04/03/2013 10:19 AM, Pawel Moll wrote: > On Tue, 2013-04-02 at 17:19 +0100, John Stultz wrote: >> But if we're going to have to do >> this via a clockid, I'm going to want it to be done via a dynamic posix >> clockid, so its clear its tightly tied with perf and not considered a >> generic interface (and I can clearly point folks having problems to the >> perf maintainers ;). > Ok, so how about the code below? > > There are two distinct parts of the "solution": > > 1. The dynamic posix clock, as you suggested. Then one can get the perf > timestamp by doing: > > clock_fd = open("/dev/perf-clock", O_RDONLY); > clock_gettime(FD_TO_CLOCKID(clock_fd), &ts) > > 2. A sort-of-hack in the get_posix_clock() function making it possible > to do the same using the perf event file descriptor, eg.: > > fd = sys_perf_event_open(&attr, -1, 0, -1, 0); > clock_gettime(FD_TO_CLOCKID(fd), &ts)
#2 makes my nose wrinkle. Forgive me for being somewhat ignorant on the perf interfaces, but why is the second portion necessary or beneficial?
thanks -john
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