sched/stats: Print domain name in /proc/schedstat

Currently, there does not exist a straightforward way to extract the
names of the sched domains and match them to the per-cpu domain entry in
/proc/schedstat other than looking at the debugfs files which are only
visible after enabling "verbose" debug after commit 3432074
("sched/debug: Put sched/domains files under the verbose flag")

Since tools like `perf sched stats`[1] require displaying per-domain
information in user friendly manner, display the names of sched domain,
alongside their level in /proc/schedstat.

Domain names also makes the /proc/schedstat data unambiguous when some
of the cpus are offline. For example, on a 128 cpus AMD Zen3 machine
where CPU0 and CPU64 are SMT siblings and CPU64 is offline:

Before:
    cpu0 ...
    domain0 ...
    domain1 ...
    cpu1 ...
    domain0 ...
    domain1 ...
    domain2 ...

After:
    cpu0 ...
    domain0 MC ...
    domain1 PKG ...
    cpu1 ...
    domain0 SMT ...
    domain1 MC ...
    domain2 PKG ...

[1] https://lore.kernel.org/lkml/[email protected]/

Signed-off-by: K Prateek Nayak <[email protected]>
Signed-off-by: Ravi Bangoria <[email protected]>
Signed-off-by: Swapnil Sapkal <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Tested-by: James Clark <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

Author: kudureranganath

kernel/sched/stats.c

@@ -138,7 +138,7 @@ static int show_schedstat(struct seq_file *seq, void *v)
 		for_each_domain(cpu, sd) {
 			enum cpu_idle_type itype;
 
-			seq_printf(seq, "domain%d %*pb", dcount++,
+			seq_printf(seq, "domain%d %s %*pb", dcount++, sd->name,
 				   cpumask_pr_args(sched_domain_span(sd)));
 			for (itype = 0; itype < CPU_MAX_IDLE_TYPES; itype++) {
 				seq_printf(seq, " %u %u %u %u %u %u %u %u %u %u %u",