On Tue, 13 Aug 2024 15:21:54 +0100
Vincent Donnefort [off-list ref] wrote:

quoted

quoted

+
+#define for_each_rb_page_desc(__pdesc, __cpu, __trace_pdesc)				\
+	for (__pdesc = (struct rb_page_desc *)&((__trace_pdesc)->__data[0]), __cpu = 0;	\
+	     __cpu < (__trace_pdesc)->nr_cpus;						\
+	     __cpu++, __pdesc = __next_rb_page_desc(__pdesc))
+
+static inline
+struct rb_page_desc *rb_page_desc(struct trace_page_desc *trace_pdesc, int cpu)
+{
+	struct rb_page_desc *pdesc;
+	int i;
+
+	if (!trace_pdesc)
+		return NULL;
+
+	for_each_rb_page_desc(pdesc, i, trace_pdesc) {
+		if (pdesc->cpu == cpu)  

Is there a reason for the linear search?

Why not just:

	if (cpu >= trace_pdesc->nr_cpus)
		return NULL;

	len = struct_size(pdesc, page_va, pdesc->nr_page_va);
	pdesc = (void *)&(trace_pdesc->__data[0]);

	return pdesc + len * cpu;

(note I don't think you need to typecast the void pointer).  

I supposed we can't assume buffers will be allocated for each CPU, hence the
need to look at each buffer.

OK, but by default that should be the fast path. We could add the above
and then do:

	pdesc += len * cpu;

	if (pdesc->cpu == cpu)
		return pdesc;

	/* Missing CPUs, need to do a linear search */

	for_each_rb_page_desc(pdesc, i, trace_pdesc) {
		if (pdesc->cpu == cpu)
	[...]

-- Steve