linux-kernel - Re: [PATCH v1 5/5] perf cs-etm: Track exception number

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Message-ID: <20181206054738.GC4244@leoy-ThinkPad-X240s>
Date:   Thu, 6 Dec 2018 13:47:38 +0800
From:   leo.yan@...aro.org
To:     Mathieu Poirier <mathieu.poirier@...aro.org>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Mike Leach <mike.leach@...aro.org>,
        Robert Walker <robert.walker@....com>,
        Al Grant <Al.Grant@....com>,
        Coresight ML <coresight@...ts.linaro.org>
Subject: Re: [PATCH v1 5/5] perf cs-etm: Track exception number

On Wed, Dec 05, 2018 at 11:03:29AM -0700, Mathieu Poirier wrote:

[...]

> > > >  static ocsd_datapath_resp_t
> > > >  cs_etm_decoder__buffer_exception(struct cs_etm_decoder *decoder,
> > > > +                            const ocsd_generic_trace_elem *elem,
> > > >                              const uint8_t trace_chan_id)
> > > >  {
> > > > -   return cs_etm_decoder__buffer_packet(decoder, trace_chan_id,
> > > > -                                        CS_ETM_EXCEPTION);
> > > > +   int ret;
> > > > +   struct cs_etm_packet *packet;
> > > > +
> > > > +   ret = cs_etm_decoder__buffer_packet(decoder, trace_chan_id,
> > > > +                                       CS_ETM_EXCEPTION);
> > > > +   if (ret != OCSD_RESP_CONT && ret != OCSD_RESP_WAIT)
> > > > +           return ret;
> > > > +
> > > > +   packet = &decoder->packet_buffer[decoder->tail];
> > > > +
> > > > +   /*
> > > > +    * Exception number is recorded per CPU and later can be used
> > > > +    * for exception return instruction analysis.
> > > > +    */
> > > > +   decoder->exc_num[packet->cpu] = elem->exception_number;
> > >
> > > Am I missing something or the information about the exception number that is
> > > recorded here isn't used anywhere?
> >
> > The exception number will be used to set branch flag patch [1].
> 
> Right, I realised that when I started reviewing that set.  The rule of
> thumb here is to introduce code in the same patchset it is used so
> that we avoid adding needless code to the kernel.

Will move this patch into sample flag series.

Thanks,
Leo Yan