linux-kernel - Re: Coresight etmv4 enable over 32bit kernel

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Message-ID: <20181211101921.GD3128@leoy-ThinkPad-X240s>
Date:   Tue, 11 Dec 2018 18:19:21 +0800
From:   leo.yan@...aro.org
To:     Lei Wen <adrian.wenl@...il.com>
Cc:     mathieu.poirier@...aro.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        leiwen@...look.com
Subject: Re: Coresight etmv4 enable over 32bit kernel

Hi Lei,

On Tue, Dec 11, 2018 at 05:11:02PM +0800, Lei Wen wrote:
> On Tue, Dec 11, 2018 at 2:02 AM Mathieu Poirier
> <mathieu.poirier@...aro.org> wrote:
> >
> > Good day Adrian,
> >
> > On Sat, 8 Dec 2018 at 05:05, Lei Wen <adrian.wenl@...il.com> wrote:
> > >
> > > Hi Mathieu,
> > >
> > > I am enabling etmv4 coresight over one Cortex-A7 soc, using 32bit kernel.
> > > And I am following [1] to do experiment regarding the addr_range feature.
> >
> > That wiki is very old and after reading it again I seriously consider
> > removing it.  It is still accurate but there are better ways to do
> > things now, i.e perf.  The main openCSD documentation page [2]
> > contains everything you need to know about the integration with perf.
> >
> > [2]. https://github.com/Linaro/OpenCSD/blob/master/HOWTO.md
> >
> > > The default addr_range is set as _stext~_etext, and it works fine with
> > > etb as sink,
> > > and etm as source. I could see there are valid kernel addresses using OpenCSD.
> >
> > I'm really curious about how you use openCSD to validate your traces -
> > can you  expand more on that?
> 
> 
> I just manually replace the cstrace.bin in the
> decoder/tests/snapshots/juno-ret-stck/.
> And modify the register data according to my platform.
> Then produce the decode result by below command:
> ./decoder/tests/bin/builddir/trc_pkt_lister -ss_dir
> decoder/tests/snapshots/test -decode -logfilename 2.ppl

Just remind, you also could refer TC2 platform, I think it can be more
close to your platform with CA7 CPUs.  And except cpu_X.ini files, you
also need to modify snapshot.ini & trace.ini under the snapshot
folder [1].

[1] https://github.com/Linaro/OpenCSD/blob/master/decoder/docs/specs/ARM%20Trace%20and%20Debug%20Snapshot%20file%20format%200v2.pdf

> > I think the results are misleading you since the openCSD library can't
> > readily be used to decode sysfs trace sessions.  The wiki doesn't
> > mention using openCSD to decode traces either.  The only integrated
> > way to use openCSD to decode CoreSight traces is via perf.  Again, the
> > link above will give you all the information you need to do that.
> 
> >
> > >
> > > But while I try to store one small range of address pair, which contain only one
> > > kernel function. It doesn't behavior like what said in [1], the write
> > > pointer would
> > > grows rapidly with the read pointer. And I dump the etb buffer and parse it with
> > > openCSD, finding that there is no I_ASYNC packet in the dump and is fulled with
> > > I_NOT_SYNC.
> > >
> > > So my question is why ETB continue to grow when there is no trigger at all?
> > > Is it normal? I could provide more info if you need it.
> >
> > I am dubious about the validation process and as such can't comment on
> > this.  Please share your results using the perf integration and then
> > I'll be able to have a better idea of what is going on.
> 
> I see... I would try use perf to get more result and get back here.

I verified mainline kernel with perf tool, it can work well on Juno
board for address range filter.  Please ensure you are using a newer
kernel version (e.g 4.16 but not 4.14, 4.14 kernel doesn't contain
cs-etm decoder in perf tool).

[...]

Thanks,
Leo Yan