Re: [PATCH] perf intel-pt: Synthesize cycle events

[Adrian Hunter]

On 15.3.2022 20.00, Steinar H. Gunderson wrote:
> On Tue, Mar 15, 2022 at 01:32:38PM +0200, Adrian Hunter wrote:
>>> I think the structure looks good, but I'm not sure about updating
>>> e.g. ptq->last_cy_insn_cnt in both functions? Does that make sense?
>> It should only be updated in the new intel_pt_synth_cycle_sample().
>> intel_pt_synth_instruction_sample() should be unchanged.
> 
> Hm, OK. But something definitely changed between my original patch and
> your change. (The first patch; I didn't try the last one yet.) With my
> patch, I got (on a specific trace, synthing cycles only with perf report
> --itrace=y0nse):
> 
> Samples: 4M of event 'cycles:uH', Event count (approx.): 4844309
> 
> With yours on the same file:
> 
> Samples: 2M of event 'cycles:uH', Event count (approx.): 77622449
> 
> The relative times between functions are also pretty different (although
> none of them are obviously crazy), so one of them has to be wrong.
> Is this to be expected, ie., would you expect your change to fix some
> bad bug on cycle-only synth? For reference, “perf script --itrace=i0ns
> -F +ipc | grep -c IPC:” (a quick proxy for the number of CYC packets :-) )
> yields 4836782, so I'm a bit surprised why there are only 2M events
> being emitted from that.

Sorry, my first suggestion has issues, but the second is better.