Re: [PATCH 2/3] powerpc: Instrument Hypervisor Calls: add wrappers

Mike Kravetz wrote:

+static inline void update_stats(unsigned long opcode, unsigned long t_before)
+{
+	unsigned long op_index = opcode >> 2;
+	struct hcall_stats *hs = &__get_cpu_var(hcall_stats[op_index]);
+
+	hs->total_time += (mftb() - t_before);
+	hs->num_calls++;
+}
+
+/*
+ * plpar_hcall wrapper
+ */
+long plpar_hcall(unsigned long opcode,
+                 unsigned long arg1,
+                 unsigned long arg2,
+                 unsigned long arg3,
+                 unsigned long arg4,
+                 unsigned long *out1,
+                 unsigned long *out2,
+                 unsigned long *out3)
+{
+	long rc;
+	unsigned long t_before;
+
+	t_before = mftb();
+	rc = plpar_hcall_base(opcode, arg1, arg2, arg3, arg4, out1, out2, out3);
+
+	update_stats(opcode, t_before);
+	return rc;
+}

Hmm, isn't it possible that the stats could be corrupted if we process
an interrupt/softirq which does an hcall while the stats are being
updated?  Maybe it's not a show-stopper, but it seems to me that
accuracy could suffer under some workloads.