Messages in this thread | | | From | Namhyung Kim <> | Subject | Re: [PATCH] perf tools: Fix JIT profiling on heap | Date | Tue, 21 Jan 2014 14:54:32 +0900 |
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Hi Arnaldo,
On Fri, 17 Jan 2014 11:34:04 -0300, Arnaldo Carvalho de Melo wrote: > Em Fri, Jan 17, 2014 at 04:44:04PM +0900, Namhyung Kim escreveu: >> On Thu, 16 Jan 2014 20:23:27 +0000, Gaurav Jain wrote: >> > On 1/16/14, 9:37 AM, "Arnaldo Carvalho de Melo" <acme@ghostprotocols.net> >> > wrote: >> > >> >>Em Thu, Jan 16, 2014 at 10:49:31AM +0900, Namhyung Kim escreveu: >> >>> Gaurav reported that perf cannot profile JIT program if it executes >> >>> the code on heap. This was because current map__new() only handle JIT >> >>> on anon mappings - extends it to handle no_dso (heap, stack) case too. >> >>> >> >>> This patch assumes JIT profiling only provides dynamic function >> >>> symbols so check the mapping type to distinguish the case. It'd >> >>> provide no symbols for data mapping - if we need to support symbols on >> >>> data mappings later it should be changed. >> >> >> >>But we do support symbols in data mappings, that is why we have >> >>MAP__VARIABLE, etc, can you elaborate? > >> > Does perf support data mappings from perf map files? Could you please >> > share an example of how I may be able to use this. > >> IIUC there's no difference between function and data mapping. So you >> can use same perf map file for both - in fact there's no way to use >> different map file in a single task. I guess perf will use it to find > > Do the /tmp/perf mapping has any per entry indication on the type of > symbol it is (data, text) like ELF and kallsyms symtabs have?
Quoting Documentation/jit-interface.txt:
Each line has the following format, fields separated with spaces:
START SIZE symbolname
START and SIZE are hex numbers without 0x. symbolname is the rest of the line, so it could contain special characters.
> > It is possible for a function and a variable to have the same virtual > address in some architectures (SPARC, iirc), that is why we have > different MAP_ types (FUNCTION, VARIABLE) (which should really be > renamed to TEXT, DATA).
Hmm.. didn't know that, interesting..
> > So a 'struct map' for a data mmap should possibly point to a different > 'dso' of the JIT /tmp/perf-... style if those maps don't have per entry > indication of text/data.
Yes, but there's no way to do it currently.
> >> only function symbols in function mappings and variables in data >> mapping based on the address it accesses. > > Well, the lookup should figure out if the IP refers to TEXT or DATA and > use MAP__{FUNCTION, VARIABLE} accordingly when asking for symbol > resolution.
Right. But in this case we cannot determine whether a symbol in the /tmp/perf-... file is a function or variable.
> >> What I wasn't sure is whether JIT program also produces some dynamic data. >> And I think only perf mem command cares about data mappings, no? > > Well, I think it would be great to do that kind of data resolution for > JITs the same way it is interesting to do for ELF ones :-) > > I need to stare harder at that patch, but with the above in mind, do we > really have to check if the map is MAP__FUNCTION as IIRC this patch > does?
Not sure. For a JIT case, I guess the mapping is always executable and we don't support data mapping yet, so it seems okay for now.
Thanks, Namhyung
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