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SubjectRe: [PATCH 8/8] perf arm-spe: Set thread TID
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On 04/02/2021 12:27, Leo Yan wrote:
> On Mon, Feb 01, 2021 at 07:40:45PM +0200, James Clark wrote:
>>
>> On 31/01/2021 14:01, Leo Yan wrote:
>>> Option 1: by merging patches 07/08 and 08/08, we can firstly support PID
>>> tracing for root namespace, and later we can extend to support PID
>>> tracing in container (and in VMs).
>>>
> Arm SPE has the problem for step2, due to the trace uses statistical
> approach, it doesn't trace the complete branch instructions, so it
> cannot promise to capture all branches for the symbol "__switch_to".
> If we only use the events PERF_RECORD_SWITCH /
> PERF_RECORD_SWITCH_CPU_WIDE, then it will lead to the coarse result
> for PID tracing.
>
> For this reason, seems to me it's pragmatic to use CONTEXTIDR for
> PID tracing at current stage, at least it can allow the root domain
> tracing works accurately. But this will leave the issue for tracing
> PID in non root namespace, we need to figure out solution later.
>
> Hi Mark.R, Al, do you have any comments for this?

Hi Leo,

I spoke with Al and his suggestion is to clear the PID value if the event
was opened outside of the root namespace.

I think that's not a bad idea as it gets us PIDs in most cases but also
doesn't show any incorrect data. Do you know if it's possible to determine
that from a perf.data file? Unfortunately it doesn't seem to be possible
to disable CONTEXTIDR tracing when opening the event as it's compile time
only and can't be disabled dynamically.

James

>
> Thanks,
> Leo
>
>>>> Signed-off-by: Leo Yan <leo.yan@linaro.org>
>>>> Signed-off-by: James Clark <james.clark@arm.com>
>>>
>>> Besides for techinical question, you could add your "Co-developed-by"
>>> tags for patches 06, 07, 08/08, which you have took time to refin them.
>>>
>>> Thanks you for kindly efforts.
>>>
>>> [1] https://lore.kernel.org/patchwork/patch/1353286/
>>>
>>>> Cc: Peter Zijlstra <peterz@infradead.org>
>>>> Cc: Ingo Molnar <mingo@redhat.com>
>>>> Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
>>>> Cc: Mark Rutland <mark.rutland@arm.com>
>>>> Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
>>>> Cc: Jiri Olsa <jolsa@redhat.com>
>>>> Cc: Namhyung Kim <namhyung@kernel.org>
>>>> Cc: John Garry <john.garry@huawei.com>
>>>> Cc: Will Deacon <will@kernel.org>
>>>> Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
>>>> Cc: Al Grant <al.grant@arm.com>
>>>> Cc: Andre Przywara <andre.przywara@arm.com>
>>>> Cc: Wei Li <liwei391@huawei.com>
>>>> Cc: Tan Xiaojun <tanxiaojun@huawei.com>
>>>> Cc: Adrian Hunter <adrian.hunter@intel.com>
>>>> ---
>>>> tools/perf/util/arm-spe.c | 75 ++++++++++++++++++++++++++-------------
>>>> 1 file changed, 50 insertions(+), 25 deletions(-)
>>>>
>>>> diff --git a/tools/perf/util/arm-spe.c b/tools/perf/util/arm-spe.c
>>>> index 27a0b9dfe22d..9828fad7e516 100644
>>>> --- a/tools/perf/util/arm-spe.c
>>>> +++ b/tools/perf/util/arm-spe.c
>>>> @@ -223,6 +223,46 @@ static inline u8 arm_spe_cpumode(struct arm_spe *spe, u64 ip)
>>>> PERF_RECORD_MISC_USER;
>>>> }
>>>>
>>>> +static void arm_spe_set_pid_tid_cpu(struct arm_spe *spe,
>>>> + struct auxtrace_queue *queue)
>>>> +{
>>>> + struct arm_spe_queue *speq = queue->priv;
>>>> + pid_t tid;
>>>> +
>>>> + tid = machine__get_current_tid(spe->machine, speq->cpu);
>>>> + if (tid != -1) {
>>>> + speq->tid = tid;
>>>> + thread__zput(speq->thread);
>>>> + } else
>>>> + speq->tid = queue->tid;
>>>> +
>>>> + if ((!speq->thread) && (speq->tid != -1)) {
>>>> + speq->thread = machine__find_thread(spe->machine, -1,
>>>> + speq->tid);
>>>> + }
>>>> +
>>>> + if (speq->thread) {
>>>> + speq->pid = speq->thread->pid_;
>>>> + if (queue->cpu == -1)
>>>> + speq->cpu = speq->thread->cpu;
>>>> + }
>>>> +}
>>>> +
>>>> +static int arm_spe_set_tid(struct arm_spe_queue *speq, pid_t tid)
>>>> +{
>>>> + int err;
>>>> + struct arm_spe *spe = speq->spe;
>>>> + struct auxtrace_queue *queue;
>>>> +
>>>> + err = machine__set_current_tid(spe->machine, speq->cpu, tid, tid);
>>>> + if (err)
>>>> + return err;
>>>> +
>>>> + queue = &speq->spe->queues.queue_array[speq->queue_nr];
>>>> + arm_spe_set_pid_tid_cpu(speq->spe, queue);
>>>> + return 0;
>>>> +}
>>>> +
>>>> static void arm_spe_prep_sample(struct arm_spe *spe,
>>>> struct arm_spe_queue *speq,
>>>> union perf_event *event,
>>>> @@ -431,6 +471,7 @@ static int arm_spe_sample(struct arm_spe_queue *speq)
>>>> static int arm_spe_run_decoder(struct arm_spe_queue *speq, u64 *timestamp)
>>>> {
>>>> struct arm_spe *spe = speq->spe;
>>>> + const struct arm_spe_record *record;
>>>> int ret;
>>>>
>>>> if (!spe->kernel_start)
>>>> @@ -450,6 +491,11 @@ static int arm_spe_run_decoder(struct arm_spe_queue *speq, u64 *timestamp)
>>>> if (ret < 0)
>>>> continue;
>>>>
>>>> + record = &speq->decoder->record;
>>>> + ret = arm_spe_set_tid(speq, record->context_id);
>>>> + if (ret)
>>>> + return ret;
>>>> +
>>>> ret = arm_spe_sample(speq);
>>>> if (ret)
>>>> return ret;
>>>> @@ -500,6 +546,10 @@ static int arm_spe__setup_queue(struct arm_spe *spe,
>>>>
>>>> record = &speq->decoder->record;
>>>>
>>>> + ret = arm_spe_set_tid(speq, record->context_id);
>>>> + if (ret)
>>>> + return ret;
>>>> +
>>>> speq->timestamp = record->timestamp;
>>>> ret = auxtrace_heap__add(&spe->heap, queue_nr, speq->timestamp);
>>>> if (ret)
>>>> @@ -552,31 +602,6 @@ static bool arm_spe__is_timeless_decoding(struct arm_spe *spe)
>>>> return timeless_decoding;
>>>> }
>>>>
>>>> -static void arm_spe_set_pid_tid_cpu(struct arm_spe *spe,
>>>> - struct auxtrace_queue *queue)
>>>> -{
>>>> - struct arm_spe_queue *speq = queue->priv;
>>>> - pid_t tid;
>>>> -
>>>> - tid = machine__get_current_tid(spe->machine, speq->cpu);
>>>> - if (tid != -1) {
>>>> - speq->tid = tid;
>>>> - thread__zput(speq->thread);
>>>> - } else
>>>> - speq->tid = queue->tid;
>>>> -
>>>> - if ((!speq->thread) && (speq->tid != -1)) {
>>>> - speq->thread = machine__find_thread(spe->machine, -1,
>>>> - speq->tid);
>>>> - }
>>>> -
>>>> - if (speq->thread) {
>>>> - speq->pid = speq->thread->pid_;
>>>> - if (queue->cpu == -1)
>>>> - speq->cpu = speq->thread->cpu;
>>>> - }
>>>> -}
>>>> -
>>>> static int arm_spe_process_queues(struct arm_spe *spe, u64 timestamp)
>>>> {
>>>> unsigned int queue_nr;
>>>> --
>>>> 2.28.0
>>>>

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