Re: [RFC PATCH] perf cs-etm: Handle valid-but-zero timestamps

On Tue, May 11, 2021 at 04:53:35PM +0300, James Clark wrote:

[...]

    /* First get the packet queue for this traceID */
    packet_queue = cs_etm__etmq_get_packet_queue(etmq, trace_chan_id);

@@ -320,7 +323,20 @@ cs_etm_decoder__do_hard_timestamp(struct cs_etm_queue *etmq, * which instructions started by subtracting the number of instructions * executed to the timestamp. */

•   packet_queue->timestamp = elem->timestamp - packet_queue->instr_count;
  

•   if (!elem->timestamp) {
  

•           packet_queue->timestamp = 0;
  

•           if (!warned_timestamp_zero) {
  

•                   pr_err("Zero Coresight timestamp found at Idx:%" OCSD_TRC_IDX_STR
  

•                           ". Decoding may be improved with --itrace=Z...\n", indx);
  

•                   warned_timestamp_zero = true;
  

•           }
  

•   }
  

•   else if (packet_queue->instr_count >= elem->timestamp) {
  

Nitpick: I personally think should use the condition ">" rather than ">=".

•           packet_queue->timestamp = 0;
  

•           pr_err("Timestamp calculation underflow at Idx:%" OCSD_TRC_IDX_STR "\n", indx);
  

•   }
  

•   else
  

•           packet_queue->timestamp = elem->timestamp - packet_queue->instr_count;
  

Nitpick for coding style, as described in Documentation/process/coding-style.rst, section "3) Placing Braces and Spaces", so here should use braces with the format:

if (!elem->timestamp) { /* print warning */ } else if {packet_queue->instr_count >= elem->timestamp) { /* print warning */ } else { packet_queue->timestamp = elem->timestamp - packet_queue->instr_count; }

Thanks, Leo

    packet_queue->next_timestamp = elem->timestamp;
    packet_queue->instr_count = 0;

@@ -542,7 +558,7 @@ cs_etm_decoder__set_tid(struct cs_etm_queue *etmq, static ocsd_datapath_resp_t cs_etm_decoder__gen_trace_elem_printer( const void *context,

•                           const ocsd_trc_index_t indx __maybe_unused,
  

•                           const ocsd_trc_index_t indx,
                            const u8 trace_chan_id __maybe_unused,
                            const ocsd_generic_trace_elem *elem)
  

{ @@ -579,7 +595,8 @@ static ocsd_datapath_resp_t cs_etm_decoder__gen_trace_elem_printer( break; case OCSD_GEN_TRC_ELEM_TIMESTAMP: resp = cs_etm_decoder__do_hard_timestamp(etmq, elem,

•                                                    trace_chan_id);
  

•                                                    trace_chan_id,
  

•                                                     indx);
            break;
    case OCSD_GEN_TRC_ELEM_PE_CONTEXT:
            resp = cs_etm_decoder__set_tid(etmq, packet_queue,
  
  
  

James

...

Thanks, Leo