> On 8 dec 2014, at 21:31, Brendan Gregg <[email protected]> wrote: > > G'Day Staffan, > > On Mon, Dec 8, 2014 at 11:17 AM, Staffan Larsen > <[email protected]> wrote: >> >>> On 8 dec 2014, at 16:05, Maynard Johnson <[email protected]> wrote: >>> > [...] >>> >>> And if the VM creates a /tmp/perf-<PID>.map file to save information about >>> JITed methods, the perf's post-profiling tool will find it and use it to >>> correlate sampled addresses it collected from the VM's executable anonymous >>> memory mappings to the method names. >> >> Is there a way in this .map file to express that different JITed methods are >> located at the same address at different times? This typically happens a lot >> when classes and their JITed methods are being unloaded from the VM. That >> space will be reused by a different method. I’m guessing this would confuse >> perf. > > In the .map file, no, at least not currently. > > However, consider the following perf sampled stack trace (this is from > my patched OpenJDK 8, with frame pointers): > > # perf record -F 99 -a -g -- sleep 10 > # perf script > [...] > java 10532 [008] 3444046.716431: cpu-clock: > 7fe919301c30 (/tmp/perf-10490.map) > 7fe91934d50c (/tmp/perf-10490.map) > 7fe9193a43d0 (/tmp/perf-10490.map) > 7fe9194ffcf0 (/tmp/perf-10490.map) > 7fe9195026d0 (/tmp/perf-10490.map) > 7fe9194ffc4c (/tmp/perf-10490.map) > 7fe91b6c440c (/tmp/perf-10490.map) > 7fe91afa9c00 (/tmp/perf-10490.map) > 7fe91ab739f4 (/tmp/perf-10490.map) > 7fe91df23630 (/tmp/perf-10490.map) > 7fe91ab739f4 (/tmp/perf-10490.map) > 7fe91acc7ea8 (/tmp/perf-10490.map) > 7fe91c4fa014 (/tmp/perf-10490.map) > 7fe9190072e0 (/tmp/perf-10490.map) > 7fe9190072e0 (/tmp/perf-10490.map) > 7fe919007325 (/tmp/perf-10490.map) > 7fe9190004e7 (/tmp/perf-10490.map) > 7fe92f70670e JavaCalls::call_helper(JavaValue*, > methodHandle*, JavaCallArguments*, Thread*) > (/mnt/openjdk8/build/linux-x86_64-normal-server-release/jdk/lib/am > 7fe92f707a3f JavaCalls::call_virtual(JavaValue*, > KlassHandle, Symbol*, Symbol*, JavaCallArguments*, Thread*) > (/mnt/openjdk8/build/linux-x86_64-normal-server-r > 7fe92f707edf JavaCalls::call_virtual(JavaValue*, Handle, > KlassHandle, Symbol*, Symbol*, Thread*) > (/mnt/openjdk8/build/linux-x86_64-normal-server-release/jdk/l > 7fe92f741668 thread_entry(JavaThread*, Thread*) > (/mnt/openjdk8/build/linux-x86_64-normal-server-release/jdk/lib/amd64/server/libjvm.so) > 7fe92fa555c8 JavaThread::thread_main_inner() > (/mnt/openjdk8/build/linux-x86_64-normal-server-release/jdk/lib/amd64/server/libjvm.so) > 7fe92fa5581c JavaThread::run() > (/mnt/openjdk8/build/linux-x86_64-normal-server-release/jdk/lib/amd64/server/libjvm.so) > 7fe92f916ba2 java_start(Thread*) > (/mnt/openjdk8/build/linux-x86_64-normal-server-release/jdk/lib/amd64/server/libjvm.so) > 7fe92ff95e9a start_thread > (/lib/x86_64-linux-gnu/libpthread-2.15.so) > > perf script emits every sampled stack trace, which I normally do for > flame graph generation. If I had Johannes's perf-map-agent loaded, > then those hex addresses become Java method symbols. > > Note the timestamp on the cpu-clock line. > > So... It should be easy to change perf-map-agent to write a > timestamped map file, to a different location (so perf doesn't find > it). Use the same timestamp type as perf. Then, a little Perl wrapper > can take "perf script" output and translate the addresses based on the > timestamped map file. (perf itself can be enhanced to do this, > although the time frame for a perf change propagating to Linux users > may be years, so the Perl wrapper could be used in the meantime.)
I see. Thanks for explaining! /Staffan > > I haven't needed to do this yet. map file churn in production has been > small (depends on workload). The real pain for us is switching apps > from Oracle JDK to my patched OpenJDK, so we get the frame pointer. > > Brendan
