Re: [PATCH v2 7/8] lib: add test for for_each_numa_{cpu,hop_mask}()

Valentin Schneider
2023-04-26T09:30:21Z

On 25/04/23 22:50, Yury Norov wrote:
> Hi Valentin,
>
> Thanks for review!
>
> On Mon, Apr 24, 2023 at 06:09:52PM +0100, Valentin Schneider wrote:
>> On 19/04/23 22:19, Yury Norov wrote:
>> > + for (node = 0; node < sched_domains_numa_levels; node++) {
>> > + unsigned int hop, c = 0;
>> > +
>> > + rcu_read_lock();
>> > + for_each_numa_cpu(cpu, hop, node, cpu_online_mask)
>> > + expect_eq_uint(cpumask_local_spread(c++, node), cpu);
>> > + rcu_read_unlock();
>> > + }
>>
>> I'm not fond of the export of sched_domains_numa_levels, especially
>> considering it's just there for tests.
>>
>> Furthermore, is there any value is testing parity with
>> cpumask_local_spread()?
>
> I wanted to emphasize that new NUMA-aware functions are coherent with
> each other, just like find_nth_bit() is coherent with find_next_bit().
>
> But all that coherence looks important only in non-NUMA case, because
> client code may depend on fact that next CPU is never less than current.
> This doesn't hold for NUMA iterators anyways...
>

Ah right, I see your point. But yes, distance-ordered walks break this
assumption.

>> Rather, shouldn't we check that using this API does
>> yield CPUs of increasing NUMA distance?
>>
>> Something like
>>
>> for_each_node(node) {
>> unsigned int prev_cpu, hop = 0;
>>
>> cpu = cpumask_first(cpumask_of_node(node));
>> prev_cpu = cpu;
>>
>> rcu_read_lock();
>>
>> /* Assert distance is monotonically increasing */
>> for_each_numa_cpu(cpu, hop, node, cpu_online_mask) {
>> expect_ge_uint(cpu_to_node(cpu), cpu_to_node(prev_cpu));
>> prev_cpu = cpu;
>> }
>>
>> rcu_read_unlock();
>> }
>
> Your version of the test looks more straightforward. I need to think
> for more, but it looks like I can take it in v3.
>

I realized I only wrote half the relevant code - comparing node IDs is
meaningless, I meant to compare distances as we walk through the
CPUs... I tested the below against a few NUMA topologies and it seems to be
sane:

diff --git a/lib/test_bitmap.c b/lib/test_bitmap.c
index 6becb044a66f0..8f8512d139d58 100644
--- a/lib/test_bitmap.c
+++ b/lib/test_bitmap.c
@@ -174,11 +174,23 @@ __check_eq_str(const char *srcfile, unsigned int line,
return eq;
}

-#define __expect_eq(suffix, ...) \
+static bool __init
+__check_ge_uint(const char *srcfile, unsigned int line,
+ const unsigned int a, unsigned int b)
+{
+ if (a < b) {
+ pr_err("[%s:%u] expected a(%u) >= b(%u)\n",
+ srcfile, line, a, b);
+ return false;
+ }
+ return true;
+}
+
+#define __expect_op(op, suffix, ...) \
({ \
int result = 0; \
total_tests++; \
- if (!__check_eq_ ## suffix(__FILE__, __LINE__, \
+ if (!__check_## op ## _ ## suffix(__FILE__, __LINE__, \
##__VA_ARGS__)) { \
failed_tests++; \
result = 1; \
@@ -186,6 +198,9 @@ __check_eq_str(const char *srcfile, unsigned int line,
result; \
})

+#define __expect_eq(suffix, ...) __expect_op(eq, suffix, ##__VA_ARGS__)
+#define __expect_ge(suffix, ...) __expect_op(ge, suffix, ##__VA_ARGS__)
+
#define expect_eq_uint(...) __expect_eq(uint, ##__VA_ARGS__)
#define expect_eq_bitmap(...) __expect_eq(bitmap, ##__VA_ARGS__)
#define expect_eq_pbl(...) __expect_eq(pbl, ##__VA_ARGS__)
@@ -193,6 +208,8 @@ __check_eq_str(const char *srcfile, unsigned int line,
#define expect_eq_clump8(...) __expect_eq(clump8, ##__VA_ARGS__)
#define expect_eq_str(...) __expect_eq(str, ##__VA_ARGS__)

+#define expect_ge_uint(...) __expect_ge(uint, ##__VA_ARGS__)
+
static void __init test_zero_clear(void)
{
DECLARE_BITMAP(bmap, 1024);
@@ -756,12 +773,23 @@ static void __init test_for_each_numa(void)
{
unsigned int cpu, node;

- for (node = 0; node < sched_domains_numa_levels; node++) {
- unsigned int hop, c = 0;
+ for_each_node(node) {
+ unsigned int start_cpu, prev_dist, hop = 0;
+
+ cpu = cpumask_first(cpumask_of_node(node));
+ prev_dist = node_distance(node, node);
+ start_cpu = cpu;

rcu_read_lock();
- for_each_numa_cpu(cpu, hop, node, cpu_online_mask)
- expect_eq_uint(cpumask_local_spread(c++, node), cpu);
+
+ /* Assert distance is monotonically increasing */
+ for_each_numa_cpu(cpu, hop, node, cpu_online_mask) {
+ unsigned int dist = node_distance(cpu_to_node(cpu), cpu_to_node(start_cpu));
+
+ expect_ge_uint(dist, prev_dist);
+ prev_dist = dist;
+ }
+
rcu_read_unlock();
}
}