(2013/09/04 17:25), Mark Wielaard wrote: > On Wed, 2013-09-04 at 15:49 +0900, Namhyung Kim wrote: >> On Tue, 03 Sep 2013 18:53:17 +0530, Hemant wrote: >>> On 09/03/2013 02:47 PM, Masami Hiramatsu wrote: >>>> Indeed, and also I'd like to know what versions of SDT this support, >>>> and where we can see the technical document of that. As far as I know, >>>> the previous(?) SDT implementation also involves ugly semaphores. >>>> Have that already gone? >> >> It seems it's not. I see the SDT v3 document still mentions semaphores. > > It mentions them, but should normally not be used. They are there for > dtrace (source) compatibility. And you don't have to use them. > > Since normally a SDT probe marker is just a NOP it doesn't have any > overhead. But if you want to add complicated arguments that you would > normally not generate in your code, then you might want to add a > semaphore. That way you can have probes with a bit more overhead that > still have zero overhead when not being probed. > > Note that if you use the normal DTRACE_PROBE macros no semaphore will be > inserted. And you can opt to not support probes that have a semaphore in > perf if you think that is easier (just check the semaphore link-time > address for the probe, it should normally be zero). Just warn: "No way I > am going to probe something that might have a little extra overhead! I > am no debugger..." :)
OK, I see. And in that case, we'd better filter out the markers which use a semaphore when list it up, since we can not enable it. Thank you, -- Masami HIRAMATSU IT Management Research Dept. Linux Technology Center Hitachi, Ltd., Yokohama Research Laboratory E-mail: masami.hiramatsu...@hitachi.com -- 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/
