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

Hello Michael,

On Fri, May 18, 2018 at 11:14:04PM +1000, Michael Ellerman wrote:

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

quoted

quoted

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@@ -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");

Is there a runtime way to check this also?  If the dmesg buffer overflows, we
lose this.

Where do you suggest we put this ? Should it be a part of
/proc/cpuinfo ?

Hmm, it'd be nice not to pollute it with more junk.

Can you just look at the pir files in sysfs?

Sure Michael. I will explore this option.

If we add a file called l1cache_thread_group, then the siblings of the
big-core that share the L1-cache can be described as follows.

	# cd  /sys/devices/system/cpu
	# grep . cpu[0-7]/l1cache_thread_group
	cpu0/l1cache_thread_group:0,2,4,6
	cpu1/l1cache_thread_group:1,3,5,7
	cpu2/l1cache_thread_group:0,2,4,6
	cpu3/l1cache_thread_group:1,3,5,7
	cpu4/l1cache_thread_group:0,2,4,6
	cpu5/l1cache_thread_group:1,3,5,7
	cpu6/l1cache_thread_group:0,2,4,6
	cpu7/l1cache_thread_group:1,3,5,7

eg. on a normal system:

  # cd /sys/devices/system/cpu
  # grep . cpu[0-7]/pir
  cpu0/pir:20
  cpu1/pir:21
  cpu2/pir:22
  cpu3/pir:23
  cpu4/pir:24
  cpu5/pir:25
  cpu6/pir:26
  cpu7/pir:27

cheers