Re: [PATCH v2 4/4] perf arm-spe: Support hardware-based PID tracing

Hi Leo,

On Wed, Nov 10, 2021 at 11:41 PM Leo Yan [off-list ref] wrote:

On Wed, Nov 10, 2021 at 11:28:48PM -0800, Namhyung Kim wrote:

[...]

quoted

quoted

+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)
+{
+       struct arm_spe *spe = speq->spe;
+       int err = machine__set_current_tid(spe->machine, speq->cpu, tid, tid);

I think we should pass -1 as pid as we don't know the real pid.

AFAICT, I observe one case for machine__set_current_tid() returning error
is 'speq->cpu' is -1 (this is the case for per-thread tracing).  In
this case, if pass '-1' for pid/tid, it still will return failure.

So here should return the error as it is.  Am I missing anything?

I'm not saying about the error.  It's about thread status.
In the machine__set_current_tid(), it calls
machine__findnew_thread() with given pid and tid.

I suspect it can set pid to a wrong value if the thread has
no pid value at the moment.

Thanks,
Namhyung

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