Re: [PATCH v1 3/5] perf cs-etm: Support for NO_SYNC packet

[Mathieu Poirier]

On Tue, 4 Dec 2018 at 20:31, <leo.yan@xxxxxxxxxx> wrote:
>
> On Mon, Nov 19, 2018 at 11:27:59AM -0700, Mathieu Poirier wrote:
> > On Sun, Nov 11, 2018 at 12:59:41PM +0800, Leo Yan wrote:
> > > As described in OpenCSD (CoreSight decoder lib), in the decoding stream
> > > it includes one trace element with type OCSD_GEN_TRC_ELEM_NO_SYNC; the
> > > element indicates 'either at start of decode, or after overflow / bad
> > > packet', we should take it as a signal for the tracing off and this will
> > > cause tracing discontinuity.  From the trace dump with 'perf script',
> > > sometimes the element OCSD_GEN_TRC_ELEM_NO_SYNC collaborates with
> > > element OCSD_GEN_TRC_ELEM_TRACE_ON to show the tracing flow have been
> > > turned off and on, in this case the cs-etm code has handled TRACE_ON
> > > packet well so we observe the tracing discontinuity; but in another case
> > > it only inserts the element OCSD_GEN_TRC_ELEM_NO_SYNC into instructions
> > > packets, we miss to handle the case if has only standalone NO_SYNC
> > > element and users cannot receive the info for tracing discontinuity.
> > >
> > > This patch introduces new type CS_ETM_TRACE_OFF to generate packet for
> > > receiving element OCSD_GEN_TRC_ELEM_NO_SYNC from decoder; when generate
> > > sample, CS_ETM_TRACE_OFF packet has almost the same behaviour with
> >
> > Here you have used the word "almost", leading me to beleive there are cases
> > where the handling of TRACE_ON and NO_SYNC packets differ, but the
> > implementation enacts the same behavior for both.
> >
> > Mike or Robert, can you confirm that TRACE_ON and NO_SYNC packets should be
> > treated the same way?
>
> I also would like to get suggestions/comments from Mike and Rob.
>
> For NO_SYNC packet, Mike before has given some explination for it:
>
> "looking at the decoder flow, when the decoder is reset, then it is
> returned to an unsynchronised state and a NO_SYNC will be output.
> With perf, it can concatenate multiple trace buffers into a single
> section of the perf.data file. To ensure that the decode process can
> see the start of a new buffer, the drivers will insert a barrier
> packet between different buffers so that the decoder can spot the
> boundaries. When the decoder hits a barrier packet it will
> automatically reset so that it correctly decodes the next trace
> buffer. This could be what you are seeing here."
>
> So I think there still have some difference between TRACE_ON and
> NO_SYNC packets, TRACE_ON packet indicates the start of trace and it's
> also possible caused by tracing discontinuity; NO_SYNC packets usually
> caused by an unsynchronised state.  But both of them presents
> discontinuity in perf trace data.
>
> I prefer to use two different packet types to present them, this can
> let the code to be more readable and easier to be maintained later.

Absolutely.  Make sure to get to the bottom of the story with Mike
and/or Robert before sending your next patchset.

>
> If you agree with this, I also will rephrase the commit log to avoid
> confusion that these two packets are the same thing.

Yes please.

>
> > Leo, if handling of the TRACE_ON and NO_SYNC packets is the same then we should
> > treat them the same way in cs_etm_decoder__gen_trace_elem_printer(), i.e simply
> > call cs_etm_decoder__buffer_trace_on().  That way packet handling in cs-etm.c
> > doesn't change.  Otherwise see my comments below.
> >
> > > CS_ETM_TRACE_ON packet: both of them invokes cs_etm__flush() to generate
> > > samples for the previous instructions packet, and in cs_etm__sample() it
> > > also needs to generate samples if TRACE_OFF packet is followed by one
> > > sequential instructions packet.  This patch also converts the address to
> > > 0 for TRACE_OFF packet, this is same with TRACE_ON packet as well.
> > >
> > > Signed-off-by: Leo Yan <leo.yan@xxxxxxxxxx>
> > > ---
> > >  tools/perf/util/cs-etm-decoder/cs-etm-decoder.c | 10 ++++++++++
> > >  tools/perf/util/cs-etm-decoder/cs-etm-decoder.h |  7 ++++---
> > >  tools/perf/util/cs-etm.c                        | 15 +++++++++++----
> > >  3 files changed, 25 insertions(+), 7 deletions(-)
> > >
> > > diff --git a/tools/perf/util/cs-etm-decoder/cs-etm-decoder.c b/tools/perf/util/cs-etm-decoder/cs-etm-decoder.c
> > > index 5efb616..9d52727 100644
> > > --- a/tools/perf/util/cs-etm-decoder/cs-etm-decoder.c
> > > +++ b/tools/perf/util/cs-etm-decoder/cs-etm-decoder.c
> > > @@ -369,6 +369,14 @@ cs_etm_decoder__buffer_range(struct cs_etm_decoder *decoder,
> > >  }
> > >
> > >  static ocsd_datapath_resp_t
> > > +cs_etm_decoder__buffer_trace_off(struct cs_etm_decoder *decoder,
> > > +                            const uint8_t trace_chan_id)
> > > +{
> > > +   return cs_etm_decoder__buffer_packet(decoder, trace_chan_id,
> > > +                                        CS_ETM_TRACE_OFF);
> > > +}
> > > +
> > > +static ocsd_datapath_resp_t
> > >  cs_etm_decoder__buffer_trace_on(struct cs_etm_decoder *decoder,
> > >                             const uint8_t trace_chan_id)
> > >  {
> > > @@ -389,6 +397,8 @@ static ocsd_datapath_resp_t cs_etm_decoder__gen_trace_elem_printer(
> > >     case OCSD_GEN_TRC_ELEM_UNKNOWN:
> > >             break;
> > >     case OCSD_GEN_TRC_ELEM_NO_SYNC:
> > > +           resp = cs_etm_decoder__buffer_trace_off(decoder,
> > > +                                                   trace_chan_id);
> >
> > If we want to handle NO_SYNC element types, why introduce a "trace_off"
> > function?  Wouldn't it make more sense to call it
> > cs_etm_decoder__buffer_no_sync() ?
>
> Will change to cs_etm_decoder__buffer_no_sync().
>
> > >             decoder->trace_on = false;
> > >             break;
> > >     case OCSD_GEN_TRC_ELEM_TRACE_ON:
> > > diff --git a/tools/perf/util/cs-etm-decoder/cs-etm-decoder.h b/tools/perf/util/cs-etm-decoder/cs-etm-decoder.h
> > > index 9351bd1..a38c97c 100644
> > > --- a/tools/perf/util/cs-etm-decoder/cs-etm-decoder.h
> > > +++ b/tools/perf/util/cs-etm-decoder/cs-etm-decoder.h
> > > @@ -23,9 +23,10 @@ struct cs_etm_buffer {
> > >  };
> > >
> > >  enum cs_etm_sample_type {
> > > -   CS_ETM_EMPTY = 0,
> > > -   CS_ETM_RANGE = 1 << 0,
> > > -   CS_ETM_TRACE_ON = 1 << 1,
> > > +   CS_ETM_EMPTY            = 0,
> > > +   CS_ETM_RANGE            = 1 << 0,
> > > +   CS_ETM_TRACE_ON         = 1 << 1,
> > > +   CS_ETM_TRACE_OFF        = 1 << 2,
> >
> > CS_ETM_NO_SYNC, see above comment.  And please don't use indentation.
>
> Will do this.
>
> > >  };
> > >
> > >  enum cs_etm_isa {
> > > diff --git a/tools/perf/util/cs-etm.c b/tools/perf/util/cs-etm.c
> > > index f4fa877..2a0cef9 100644
> > > --- a/tools/perf/util/cs-etm.c
> > > +++ b/tools/perf/util/cs-etm.c
> > > @@ -517,8 +517,9 @@ static inline int cs_etm__t32_instr_size(struct cs_etm_queue *etmq,
> > >
> > >  static inline u64 cs_etm__first_executed_instr(struct cs_etm_packet *packet)
> > >  {
> > > -   /* Returns 0 for the CS_ETM_TRACE_ON packet */
> > > -   if (packet->sample_type == CS_ETM_TRACE_ON)
> > > +   /* Returns 0 for TRACE_ON and TRACE_OFF packets */
> > > +   if (packet->sample_type == CS_ETM_TRACE_ON ||
> > > +       packet->sample_type == CS_ETM_TRACE_OFF)
> > >             return 0;
> > >
> > >     return packet->start_addr;
> > > @@ -527,8 +528,9 @@ static inline u64 cs_etm__first_executed_instr(struct cs_etm_packet *packet)
> > >  static inline
> > >  u64 cs_etm__last_executed_instr(const struct cs_etm_packet *packet)
> > >  {
> > > -   /* Returns 0 for the CS_ETM_TRACE_ON packet */
> > > -   if (packet->sample_type == CS_ETM_TRACE_ON)
> > > +   /* Returns 0 for TRACE_ON and TRACE_OFF packets */
> > > +   if (packet->sample_type == CS_ETM_TRACE_ON ||
> > > +       packet->sample_type == CS_ETM_TRACE_OFF)
> > >             return 0;
> > >
> > >     return packet->end_addr - packet->last_instr_size;
> > > @@ -930,6 +932,10 @@ static int cs_etm__sample(struct cs_etm_queue *etmq)
> > >             if (etmq->prev_packet->sample_type == CS_ETM_TRACE_ON)
> > >                     generate_sample = true;
> > >
> > > +           /* Generate sample for tracing off packet */
> > > +           if (etmq->prev_packet->sample_type == CS_ETM_TRACE_OFF)
> > > +                   generate_sample = true;
> > > +
> > >             /* Generate sample for branch taken packet */
> > >             if (etmq->prev_packet->sample_type == CS_ETM_RANGE &&
> > >                 etmq->prev_packet->last_instr_taken_branch)
> > > @@ -1085,6 +1091,7 @@ static int cs_etm__run_decoder(struct cs_etm_queue *etmq)
> > >                                     cs_etm__sample(etmq);
> > >                                     break;
> > >                             case CS_ETM_TRACE_ON:
> > > +                           case CS_ETM_TRACE_OFF:
> > >                                     /*
> > >                                      * Discontinuity in trace, flush
> > >                                      * previous branch stack
> > > --
> > > 2.7.4
> > >