Re: [PATCH 1/2] powerpc: Detect the presence of big-core with interleaved threads

Hello Michael,

On Fri, May 18, 2018 at 11:21:22PM +1000, Michael Ellerman wrote:

"Gautham R. Shenoy" [off-list ref] writes:

quoted

diff --git a/arch/powerpc/kernel/setup-common.c b/arch/powerpc/kernel/setup-common.c
index 0af5c11..884dff2 100644
--- a/arch/powerpc/kernel/setup-common.c
+++ b/arch/powerpc/kernel/setup-common.c

@@ -436,8 +438,56 @@ static void __init cpu_init_thread_core_maps(int tpc)
 	printk(KERN_DEBUG " (thread shift is %d)\n", threads_shift);
 }
 
-
 u32 *cpu_to_phys_id = NULL;
+/*
+ * check_for_interleaved_big_core - Checks if the core represented by
+ *	 dn is a big-core whose threads are interleavings of the
+ *	 threads of the component small cores.
+ *
+ * @dn: device node corresponding to the core.
+ *
+ * Returns true if the core is a interleaved big-core.
+ * Returns false otherwise.
+ */
+static inline bool check_for_interleaved_big_core(struct device_node *dn)
+{
+	int len, nr_groups, threads_per_group;
+	const __be32 *thread_groups;
+	__be32 *thread_list, *first_cpu_idx;
+	int cur_cpu, next_cpu, i, j;
+
+	thread_groups = of_get_property(dn, "ibm,thread-groups", &len);
+	if (!thread_groups)
+		return false;

There are better device tree APIs than bare of_get_property() these
days, can you try to use those?

Ok, I will use them.

quoted

+	nr_groups = be32_to_cpu(*(thread_groups + 1));
+	if (nr_groups <= 1)
+		return false;

eg. this would be of_property_read_u32_index()

Ok.

quoted

@@ -565,7 +615,16 @@ void __init smp_setup_cpu_maps(void)
 	vdso_data->processorCount = num_present_cpus();
 #endif /* CONFIG_PPC64 */
 
-        /* Initialize CPU <=> thread mapping/
+	dn = of_find_node_by_type(NULL, "cpu");
+	if (dn) {
+		if (check_for_interleaved_big_core(dn)) {
+			has_interleaved_big_core = true;
+			pr_info("Detected interleaved big-cores\n");
+		}
+		of_node_put(dn);
+	}

This is a bit untidy, given how unlikely it is that you would have no
CPUs :)

This can actually go into the earlier loop where we initialize the
smp_processor_ids(). I have fixed it in the next iteration.

You should be able to do the lookup of the property and the setting of
has_interleaved_big_core all inside
check_for_interleaved_big_core().

Yes, that's what I am doing in the next iteration.

cheers