Re: [PATCH] perf jvmti: remove redundant jitdump line table entries

[Nick Gasson <nick.gasson@arm.com>]

On 05/28/20 02:08 AM, Ian Rogers wrote:
>>
>> I noticed it loses information when the Hotspot code cache is
>> resized. I've been working around that by setting
>> -XX:InitialCodeCacheSize and -XX:ReservedCodeCacheSize to large
>> values. Does this help in your case?
>
> Thanks, I tried and also with Steve's patch:
> https://lore.kernel.org/lkml/1590544271-125795-1-git-send-email-steve.maclean@linux.microsoft.com/

Thanks for the reference! That patch fixes the problem I had with code
cache resizing so the workaround above is no longer necessary.

>
> Trying something very basic like just the -version command with compile only:
> /tmp/perf/perf record -k 1 -e cycles:u -F 6500 -o /tmp/perf.data java
> -agentpath:/tmp/perf/libperf-jvmti.so -XX:+PreserveFramePointer
> -XX:InitialCodeCacheSize=2G -XX:ReservedCodeCacheSize=2G
> -XX:CompileOnly=1 -version
> /tmp/perf/perf inject -i /tmp/perf.data -o /tmp/perf-jit.data -j
> /tmp/perf/perf report -i /tmp/perf-jit.data
>
> I don't see any of the JDK classes but 35 unknown symbols out of 272.
> The JDK classes are stripped to some degree iirc, but we should be
> able to give a symbol name as we don't care about local variables and
> like.
>

I tried this with latest perf/core and JDK 11 but I don't see any
[unknown] from jitted-*.so. All the events are in "Interpreter": I think
the options you want are -Xcomp -Xbatch rather than -XX:CompileOnly=1?
The latter restricts compilation to the named method/package.

There was a bug where no jitdump debug info was written for classes
compiled without line tables. That was fixed by d3ea46da3 ("perf jvmti:
Fix jitdump for methods without debug info").

--
Nick