perf tools: Add guest_cpu to hypervisor threads

It is possible to know which guest machine was running at a point in time
based on the PID of the currently running host thread. That is, perf
identifies guest machines by the PID of the hypervisor.

To determine the guest CPU, put it on the hypervisor (QEMU) thread for
that VCPU.

This is done when processing the id_index which provides the necessary
information.

Signed-off-by: Adrian Hunter <[e-mail]>
Cc: Andi Kleen <[e-mail]>
Cc: Ian Rogers <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: [e-mail]
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/util/session.c

···
 	return 0;
 }
 
+static int perf_session__set_guest_cpu(struct perf_session *session, pid_t pid,
+				       pid_t tid, int guest_cpu)
+{
+	struct machine *machine = &session->machines.host;
+	struct thread *thread = machine__findnew_thread(machine, pid, tid);
+
+	if (!thread)
+		return -ENOMEM;
+	thread->guest_cpu = guest_cpu;
+	thread__put(thread);
+
+	return 0;
+}
+
 int perf_event__process_id_index(struct perf_session *session,
 				 union perf_event *event)
 {
···
 			last_pid = sid->machine_pid;
 			perf_guest = true;
 		}
+
+		ret = perf_session__set_guest_cpu(session, sid->machine_pid, e->tid, e2->vcpu);
+		if (ret)
+			return ret;
 	}
 	return 0;
 }

tools/perf/util/thread.c

···
 		thread->tid = tid;
 		thread->ppid = -1;
 		thread->cpu = -1;
+		thread->guest_cpu = -1;
 		thread->lbr_stitch_enable = false;
 		INIT_LIST_HEAD(&thread->namespaces_list);
 		INIT_LIST_HEAD(&thread->comm_list);

tools/perf/util/thread.h

···
 	pid_t			tid;
 	pid_t			ppid;
 	int			cpu;
+	int			guest_cpu; /* For QEMU thread */
 	refcount_t		refcnt;
 	bool			comm_set;
 	int			comm_len;