Re: [PATCH v2] perf arm-spe: Synthesize SPE instruction events

[German Gomez]

Hi Leo,

Thanks for your comments. I'll send a revised patch shortly.

Thanks,
German

On 16/12/2021 11:11, Leo Yan wrote:
> Hi German,
>
> On Wed, Dec 15, 2021 at 06:46:05PM +0000, German Gomez wrote:
>> Synthesize instruction events per every decoded ARM SPE record.
>>
>> Because Arm SPE implements a hardware-based sample period, and perf
>> implements a software-based one that gets applied on top, also add a
>> warning to make the user aware.
>>
>> Signed-off-by: German Gomez <german.gomez@xxxxxxx>
>> ---
>> Changes since v1 [https://lore.kernel.org/all/20211117142833.226629-1-german.gomez@xxxxxxx]
>>   - Generate events with "--itrace=i" instead of "--itrace=o".
>>   - Generate events with virt_addr, phys_addr, and data_src values.
>> ---
>>  tools/perf/util/arm-spe.c | 58 +++++++++++++++++++++++++++++++++++++++
>>  1 file changed, 58 insertions(+)
>>
>> diff --git a/tools/perf/util/arm-spe.c b/tools/perf/util/arm-spe.c
>> index fccac06b573a..879583822c8f 100644
>> --- a/tools/perf/util/arm-spe.c
>> +++ b/tools/perf/util/arm-spe.c
>> @@ -58,6 +58,8 @@ struct arm_spe {
>>  	u8				sample_branch;
>>  	u8				sample_remote_access;
>>  	u8				sample_memory;
>> +	u8				sample_instructions;
>> +	u64				instructions_sample_period;
>>  
>>  	u64				l1d_miss_id;
>>  	u64				l1d_access_id;
>> @@ -68,6 +70,7 @@ struct arm_spe {
>>  	u64				branch_miss_id;
>>  	u64				remote_access_id;
>>  	u64				memory_id;
>> +	u64				instructions_id;
>>  
>>  	u64				kernel_start;
>>  
>> @@ -90,6 +93,7 @@ struct arm_spe_queue {
>>  	u64				time;
>>  	u64				timestamp;
>>  	struct thread			*thread;
>> +	u64				period_instructions;
>>  };
>>  
>>  static void arm_spe_dump(struct arm_spe *spe __maybe_unused,
>> @@ -202,6 +206,7 @@ static struct arm_spe_queue *arm_spe__alloc_queue(struct arm_spe *spe,
>>  	speq->pid = -1;
>>  	speq->tid = -1;
>>  	speq->cpu = -1;
>> +	speq->period_instructions = 0;
>>  
>>  	/* params set */
>>  	params.get_trace = arm_spe_get_trace;
>> @@ -351,6 +356,33 @@ static int arm_spe__synth_branch_sample(struct arm_spe_queue *speq,
>>  	return arm_spe_deliver_synth_event(spe, speq, event, &sample);
>>  }
>>  
>> +static int arm_spe__synth_instruction_sample(struct arm_spe_queue *speq,
>> +					     u64 spe_events_id, u64 data_src)
>> +{
>> +	struct arm_spe *spe = speq->spe;
>> +	struct arm_spe_record *record = &speq->decoder->record;
>> +	union perf_event *event = speq->event_buf;
>> +	struct perf_sample sample = { .ip = 0, };
>> +
>> +	/*
>> +	 * Handles perf instruction sampling period.
>> +	 */
>> +	speq->period_instructions++;
>> +	if (speq->period_instructions < spe->instructions_sample_period)
>> +		return 0;
>> +	speq->period_instructions = 0;
>> +
>> +	arm_spe_prep_sample(spe, speq, event, &sample);
>> +
>> +	sample.id = spe_events_id;
>> +	sample.stream_id = spe_events_id;
>> +	sample.addr = record->virt_addr;
>> +	sample.phys_addr = record->phys_addr;
>> +	sample.data_src = data_src;
>> +
>> +	return arm_spe_deliver_synth_event(spe, speq, event, &sample);
>> +}
>> +
>>  #define SPE_MEM_TYPE	(ARM_SPE_L1D_ACCESS | ARM_SPE_L1D_MISS | \
>>  			 ARM_SPE_LLC_ACCESS | ARM_SPE_LLC_MISS | \
>>  			 ARM_SPE_REMOTE_ACCESS)
>> @@ -480,6 +512,12 @@ static int arm_spe_sample(struct arm_spe_queue *speq)
>>  			return err;
>>  	}
>>  
>> +	if (spe->sample_instructions) {
>> +		err = arm_spe__synth_instruction_sample(speq, spe->instructions_id, data_src);
>> +		if (err)
>> +			return err;
>> +	}
>> +
>>  	return 0;
>>  }
>>  
>> @@ -1107,6 +1145,26 @@ arm_spe_synth_events(struct arm_spe *spe, struct perf_session *session)
>>  			return err;
>>  		spe->memory_id = id;
>>  		arm_spe_set_event_name(evlist, id, "memory");
>> +		id += 1;
>> +	}
>> +
>> +	if (spe->synth_opts.instructions) {
>> +		if (spe->synth_opts.period_type != PERF_ITRACE_PERIOD_INSTRUCTIONS)
>> +			return -EINVAL;
> Will this break some perf commands, like "perf report" or other perf
> report commands?
>
> See the the function arm_spe_process_auxtrace_info(), it invokes [1]:
>
>     itrace_synth_opts__set_default(&spe->synth_opts, false);
>
> So synth_opts.instructions is initialized to true,
> synth_opts.period_type is set to PERF_ITRACE_DEFAULT_PERIOD_TYPE (2),
> so the perf tool will directly bail out when synth_opts.period_type is
> not equal to PERF_ITRACE_PERIOD_INSTRUCTIONS.
>
> If we only support period type PERF_ITRACE_PERIOD_INSTRUCTIONS at
> current stage, I think we use the checking like below:
>
>   if (spe->synth_opts.instructions &&
>       (spe->synth_opts.period_type == PERF_ITRACE_PERIOD_INSTRUCTIONS)) {
>
>      ...
>   }
>
> [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/perf/util/arm-spe.c#n1180
>
>> +
>> +		if (spe->synth_opts.period > 1)
>> +			pr_warning("Arm SPE has a hardware-based sample period.\n"
>> +				   "More instruction events will be discarded by --itrace\n");
> Okay, Since Arm SPE is statistical profiling, so this is the right thing to
> do.
>
> Please also address Namhyung's two comments, the rest of this patch looks
> good to me.
>
> Thanks,
> Leo
>
>> +
>> +		spe->sample_instructions = true;
>> +		attr.config = PERF_COUNT_HW_INSTRUCTIONS;
>> +		attr.sample_period = spe->synth_opts.period;
>> +		spe->instructions_sample_period = attr.sample_period;
>> +		err = arm_spe_synth_event(session, &attr, id);
>> +		if (err)
>> +			return err;
>> +		spe->instructions_id = id;
>> +		arm_spe_set_event_name(evlist, id, "instructions");
>>  	}
>>  
>>  	return 0;
>> -- 
>> 2.25.1
>>