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Date: Mon, 18 Oct 2021 12:01:27 +0100
From: German Gomez <german.gomez@....com>
To: Leo Yan <leo.yan@...aro.org>, Namhyung Kim <namhyung@...nel.org>,
James Clark <james.clark@....com>
Cc: Arnaldo Carvalho de Melo <acme@...nel.org>,
Jiri Olsa <jolsa@...hat.com>, Ingo Molnar <mingo@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
LKML <linux-kernel@...r.kernel.org>,
Andi Kleen <ak@...ux.intel.com>,
Ian Rogers <irogers@...gle.com>,
Stephane Eranian <eranian@...gle.com>,
Adrian Hunter <adrian.hunter@...el.com>
Subject: Re: [RFC] perf arm-spe: Track task context switch for cpu-mode events
Hi,
What do you thing of the patch below? PERF_RECORD_SWITCH events are also
included for tracing forks. The patch would sit on top of Namhyung's.
Thanks,
German
On 12/10/2021 12:07, German Gomez wrote:
> Hi, Leo and Namhyung,
>
> I want to make sure I'm on the same page as you regarding this topic.
>
> [...]
>
> If we are not considering patching the driver at this stage, so we allow
> hardware tracing on non-root namespaces. I think we could proceed like
> this:
>
> - For userspace, always use context-switch events as they are
> accurate and consistent with namespaces.
> - For kernel tracing, if context packets are enabled, use them, but
> warn the user that the PIDs correspond to the root namespace.
> - Otherwise, use context-switch events and warn the user of the time
> inaccuracies.
>
> Later, if the driver is patched to disable context packets outside the
> root namespace, kernel tracing could fall back to using context-switch
> events and warn the user with a single message about the time
> inaccuracies.
>
> If we are aligned, we could collect your feedback and share an updated
> patch that considers the warnings.
>
> Many thanks
> Best regards
---
tools/perf/util/arm-spe.c | 66 +++++++++++++++++++++++++++++++++++++--
1 file changed, 63 insertions(+), 3 deletions(-)
diff --git a/tools/perf/util/arm-spe.c b/tools/perf/util/arm-spe.c
index 708323d7c93c..6a2f7a484a80 100644
--- a/tools/perf/util/arm-spe.c
+++ b/tools/perf/util/arm-spe.c
@@ -71,6 +71,17 @@ struct arm_spe {
u64 kernel_start;
unsigned long num_events;
+
+ /*
+ * Used for PID tracing.
+ */
+ u8 exclude_kernel;
+
+ /*
+ * Warning messages.
+ */
+ u8 warn_context_pkt_namesapce;
+ u8 warn_context_switch_ev_accuracy;
};
struct arm_spe_queue {
@@ -586,11 +597,42 @@ static bool arm_spe__is_timeless_decoding(struct arm_spe *spe)
return timeless_decoding;
}
+static bool arm_spe__is_exclude_kernel(struct arm_spe *spe) {
+ struct evsel *evsel;
+ struct evlist *evlist = spe->session->evlist;
+
+ evlist__for_each_entry(evlist, evsel) {
+ if (evsel->core.attr.type == spe->pmu_type && evsel->core.attr.exclude_kernel)
+ return true;
+ }
+
+ return false;
+}
+
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;
+ pid_t tid = machine__get_current_tid(spe->machine, speq->cpu);
+ u64 context_id = speq->decoder->record.context_id;
+
+ /*
+ * We're tracing the kernel.
+ */
+ if (!spe->exclude_kernel) {
+ /*
+ * Use CONTEXT packets in kernel tracing if available and warn the user of the
+ * values correspond to the root PID namespace.
+ *
+ * If CONTEXT packets aren't available but context-switch events are, warn the user
+ * of the time inaccuracies.
+ */
+ if (context_id != (u64) -1) {
+ tid = speq->decoder->record.context_id;
+ spe->warn_context_pkt_namesapce = true;
+ } else if (tid != -1 && context_id == (u64) -1)
+ spe->warn_context_switch_ev_accuracy = true;
+ }
tid = machine__get_current_tid(spe->machine, speq->cpu);
if (tid != -1) {
@@ -740,7 +782,8 @@ static int arm_spe_process_event(struct perf_session *session,
if (err)
return err;
- if (event->header.type == PERF_RECORD_SWITCH_CPU_WIDE)
+ if (event->header.type == PERF_RECORD_SWITCH_CPU_WIDE ||
+ event->header.type == PERF_RECORD_SWITCH)
err = arm_spe_context_switch(spe, event, sample);
}
@@ -807,7 +850,20 @@ static int arm_spe_flush(struct perf_session *session __maybe_unused,
return arm_spe_process_timeless_queues(spe, -1,
MAX_TIMESTAMP - 1);
- return arm_spe_process_queues(spe, MAX_TIMESTAMP);
+ ret = arm_spe_process_queues(spe, MAX_TIMESTAMP);
+
+ if (spe->warn_context_pkt_namesapce)
+ ui__warning(
+ "Arm SPE CONTEXT packets used for PID/TID tracing.\n\n"
+ "PID values correspond to the root PID namespace.\n\n");
+
+ if (spe->warn_context_switch_ev_accuracy)
+ ui__warning(
+ "No Arm SPE CONTEXT packets found within traces.\n\n"
+ "Fallback to PERF_RECORD_SWITCH events for PID/TID tracing will have\n"
+ "workload-dependant timing inaccuracies.\n\n");
+
+ return ret;
}
static void arm_spe_free_queue(void *priv)
@@ -1083,6 +1139,10 @@ int arm_spe_process_auxtrace_info(union perf_event *event,
spe->timeless_decoding = arm_spe__is_timeless_decoding(spe);
+ spe->exclude_kernel = arm_spe__is_exclude_kernel(spe);
+ spe->warn_context_pkt_namesapce = false;
+ spe->warn_context_switch_ev_accuracy = false;
+
/*
* The synthesized event PERF_RECORD_TIME_CONV has been handled ahead
* and the parameters for hardware clock are stored in the session
--
2.17.1
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