Messages in this thread | | | Date | Thu, 28 Apr 2016 01:46:12 +0530 | From | Hemant Kumar <> | Subject | Re: [PATCH perf/core v4 14/19] perf buildid-cache: Scan and import user SDT events to probe cache |
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On 04/27/2016 08:58 PM, Arnaldo Carvalho de Melo wrote: > Em Wed, Apr 27, 2016 at 08:49:08PM +0530, Hemant Kumar escreveu: >> >> On 04/26/2016 02:34 PM, Masami Hiramatsu wrote: >>> From: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com> >>> >>> perf buildid-cache --add <binary> scans given binary and add >>> the SDT events to probe cache. "sdt_" prefix is appended for >>> all SDT providers to avoid event-name clash with other pre-defined >>> events. It is possible to use the cached SDT events as other cached >>> events, via perf probe --add "sdt_<provider>:<event>=<event>". >>> >>> e.g. >>> ---- >>> # perf buildid-cache --add /lib/libc-2.17.so >>> # perf probe --cache --list | head -n 5 >>> /usr/lib/libc-2.17.so (a6fb821bdf53660eb2c29f778757aef294d3d392): >>> sdt_libc:setjmp=setjmp >>> sdt_libc:longjmp=longjmp >>> sdt_libc:longjmp_target=longjmp_target >>> sdt_libc:memory_heap_new=memory_heap_new >>> # perf probe -x /usr/lib/libc-2.17.so \ >>> -a sdt_libc:memory_heap_new=memory_heap_new >>> Added new event: >>> sdt_libc:memory_heap_new (on memory_heap_new >>> in /usr/lib/libc-2.17.so) >>> >>> You can now use it in all perf tools, such as: >>> >>> perf record -e sdt_libc:memory_heap_new -aR sleep 1 >>> >>> # perf probe -l >>> sdt_libc:memory_heap_new (on new_heap+183 in /usr/lib/libc-2.17.so) >>> ---- >> Patch looks good to me. Have a few questions below : >> >> What about the same binary path having different build-ids. For e.g >> a binary say, "test" has some markers, we add it to the cache. And, >> then the file gets rebuilt again with different build-id now. And we try >> to add to the cache again. It shows multiple entries in the cache : >> # perf probe --cache --list >> /home/hemant/test (157380727e2b3854395aa915dfc91dbccc02058b): >> sdt_user_test:marker1=marker1 >> /home/hemant/test (64c0a018636e6d5145b09fc65839c1a4a7899f18): >> sdt_user_test:marker1=marker1 >> /home/hemant/test (c9e34759ae95b68fa385831041c5d9e0dd1697fb): >> sdt_user_test:marker1=marker1 >> ... >> >> But, perf list sdt shows only one entry (which it should) : >> # perf list sdt >> >> List of pre-defined events (to be used in -e): >> >> sdt_user_test:marker1 [SDT event] >> >> perf probe also works as expected : >> # perf probe -x /home/hemant/test %sdt_user_test:marker1 >> Added new event: >> sdt_user_test:marker1 (on %marker1 in /home/hemant/test) >> >> You can now use it in all perf tools, such as: >> >> perf record -e sdt_user_test:marker1 -aR sleep 1 >> >> So, the question is, do we delete the previous entries for "test" from >> the cache once we get a newer version of "test"? > No, we shouldn't, since those entries may be used for other tasks that > involves using the exact DSO used for a particular perf.data session. > > Humm, but you are talking about what cache? The "probe cache" or the > "build-id cache"? My previous statement was about the build-id cache.
I was talking about the "probe cache".
> For the probe cache, humm, probably we want to keep it as well, we may > have moved that 'test' file to some other place, renamed it, etc, but it > continues being accessible by its content-based identifier (the > build-id) and could be used in ways we don't envision right now.
Agreed. Makes sense.
> I.e. the same principle used for the build-id cache should be used for > this probe cache, where we store things by build-id. > > We need to prune this from time to time and for this we have: > > perf buildid-cache purge > > But that right now is unflexible, we should have a way to ask to control > how much is purged :-\
Right.
-- Thanks, Hemant Kumar
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