linux-kernel - Re: [PATCH/RFC] perf buildid: Cache kernel DSO created when reading buildid header table

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Date:	Fri, 25 Sep 2015 14:54:52 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:	Adrian Hunter <adrian.hunter@...el.com>,
	Borislav Petkov <bp@...e.de>, David Ahern <dsahern@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Jiri Olsa <jolsa@...hat.com>,
	Stephane Eranian <eranian@...gle.com>,
	Wang Nan <wangnan0@...wei.com>, Ingo Molnar <mingo@...nel.org>,
	平松雅巳 / HIRAMATU，MASAMI 
	<masami.hiramatsu.pt@...achi.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH/RFC] perf buildid: Cache kernel DSO created when reading
 buildid header table

On Thu, Sep 24, 2015 at 12:56:31PM -0300, Arnaldo Carvalho de Melo wrote:
> Em Fri, Sep 25, 2015 at 12:01:12AM +0900, Namhyung Kim escreveu:
> > Hi Arnaldo,
> > 
> > On Thu, Sep 24, 2015 at 10:42:28AM -0300, Arnaldo Carvalho de Melo wrote:
> > > Namhyung,
> > > 
> > > 	Can you take a look and perhaps give me your Acked-by?
> > 
> > The dso->kernel and event->cpumode is always confusing for modules..
> 
> Right, my idea is to delete dso->kernel, to remove this confusion.

I'm fine with that. :)


> 
> Please see my tmp.perf/core branch, there are a few patches there using
> alternative methods in places previously using the botched dso->kernel.
> 
> > In this case, it seems that mmap events set kernel cpumode but
> > build-id events don't.
> 
> in the previous sentence you think build-id events don't set
> perf_event_attr.misc bits related to cpumode...
> 
> > So kernel cpumode in a bulid-id event
> > indicates that it is a kernel (vmlinux) dso, right?
> 
> While here you ask if it does?

I mean that cpumode is not set for modules, so if you see cpumode set,
it should be the kernel dso..


> 
> All these are synthesized, it is a matter of looking at the routines
> synthesizing them :-)

Right.


> 
> > I'll test this tomorrow..
> 
> Thanks, over time there were areas where multiple people touched and
> added different semantics that are biting now, I'm trying to, while
> fixing a bug, the one Wang Nan reported, clarify those things.
> 
> It is taking more time than I antecipated, as I'm stumbling in what look
> like other bugs in the perf-probe codebase :-/

OK, after applying this patch, perf cannot find vmlinux anymore.  It
finds scsi_mod.ko.gz instead, resulting in no kernel symbols..

Before:

  $ perf report | grep -F '[k]' | head
   0.44%  cc1              [kernel.vmlinux]               [k] clear_page_c
   0.34%  cc1              [kernel.vmlinux]               [k] page_fault
   0.22%  cc1              [kernel.vmlinux]               [k] get_page_from_freelist
   0.22%  cc1              [kernel.vmlinux]               [k] handle_mm_fault
   0.15%  cc1              [kernel.vmlinux]               [k] __do_page_fault
   0.13%  cc1              [kernel.vmlinux]               [k] unmap_single_vma
   0.12%  cc1              [kernel.vmlinux]               [k] __mem_cgroup_count_vm_event
   0.11%  cc1              [kernel.vmlinux]               [k] mem_cgroup_try_charge
   0.11%  cc1              [kernel.vmlinux]               [k] __d_lookup_rcu
   0.11%  cc1              [kernel.vmlinux]               [k] copy_user_generic_string    

After: (same data file but having no symbol affects the result)

  $ perf report | grep -F '[k]' | head
   0.42%  cc1              scsi_mod.ko.gz                 [k] 0xffffffff812b4077
   0.33%  cc1              scsi_mod.ko.gz                 [k] 0xffffffff8153f9d0
   0.11%  cc1              scsi_mod.ko.gz                 [k] 0xffffffff8117ec0c
   0.10%  cc1              scsi_mod.ko.gz                 [k] 0xffffffff812b443c
   0.10%  as               scsi_mod.ko.gz                 [k] 0xffffffff812b4077
   0.08%  cc1              scsi_mod.ko.gz                 [k] 0xffffffff811bbd90
   0.07%  cc1              scsi_mod.ko.gz                 [k] 0xffffffff811bf188
   0.07%  as               scsi_mod.ko.gz                 [k] 0xffffffff8153f9d0
   0.06%  sh               scsi_mod.ko.gz                 [k] 0xffffffff8153f9d0
   0.06%  cc1              scsi_mod.ko.gz                 [k] 0xffffffff811e0838                       


Unfortunately, I don't have to time to look at it now.  It's one of
the biggest national holiday in Korea so maybe I can have a look later
in next week.

Thanks,
Namhyung
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