[PATCH i-g-t] tests/intel/perf_pmu: Drop cpu-hotplug subtest

[Lucas De Marchi]

This test has been skipping since a long time (forever?) in CI. The
reason is that cpu0 is not really hot pluggable. There was an initial
attempt that got removed with kernel commits 5475abbde77f ("x86/smpboot:
Remove the CPU0 hotplug kludge") and e59e74dc48a3 ("x86/topology: Remove
CPU0 hotplug option").

With those commits there are no more cpu0_hotplug kernel parameter and
no more BOOTPARAM_HOTPLUG_CPU0 build config.

The current i915 pmu integration always returns the first cpu in the
system, which means that it's always cpu0.  The cpu migration is also
currently wrong and was never detected by this test: it tries to find a
sibling cpu rather than allowing to migrate to any cpu in the system.
In order to clean up the i915 side, the hotplug code is being removed in
favor of the generic one, provided by perf infra. That too has the same
"issue" that there's no easy way to test, but hopefully receives more
visibility since it's shared by several drivers.

If we ever find a way to instrument the kernel to test the hotplug, this
code can be partially restored.

References: https://lore.kernel.org/all/20250116222426.77757-1-lucas.demarchi@intel.com/
Signed-off-by: Lucas De Marchi <lucas.demarchi at intel.com>
---
 tests/intel/perf_pmu.c | 142 -----------------------------------------
 1 file changed, 142 deletions(-)

diff --git a/tests/intel/perf_pmu.c b/tests/intel/perf_pmu.c
index 5d0467c02..084ef9631 100644
--- a/tests/intel/perf_pmu.c
+++ b/tests/intel/perf_pmu.c
@@ -101,9 +101,6 @@
  * SUBTEST: busy-start
  * Description: Test to verify gpu busyness through engine business pmu counters
  *
- * SUBTEST: cpu-hotplug
- * Description: Test the i915 pmu perf interface
- *
  * SUBTEST: enable-race
  * Description: Test the i915 pmu perf interface
  *
@@ -1362,139 +1359,6 @@ static void open_invalid(int i915)
 	igt_assert_lt(fd, 0);
 }
 
-static bool cpu0_hotplug_support(void)
-{
-	return access("/sys/devices/system/cpu/cpu0/online", W_OK) == 0;
-}
-
-static void cpu_hotplug(int gem_fd)
-{
-	igt_spin_t *spin[2];
-	uint64_t ts[2];
-	uint64_t val;
-	int link[2];
-	int fd, ret;
-	int cur = 0;
-	char buf;
-	uint64_t ahnd = get_reloc_ahnd(gem_fd, 0);
-
-	igt_require(cpu0_hotplug_support());
-
-	fd = open_pmu(gem_fd,
-		      I915_PMU_ENGINE_BUSY(I915_ENGINE_CLASS_RENDER, 0));
-
-	/*
-	 * Create two spinners so test can ensure shorter gaps in engine
-	 * busyness as it is terminating one and re-starting the other.
-	 */
-	spin[0] = igt_spin_new(gem_fd, .ahnd = ahnd,
-			       .engine = I915_EXEC_DEFAULT);
-	spin[1] = __igt_spin_new(gem_fd, .ahnd = ahnd,
-				 .engine = I915_EXEC_DEFAULT);
-
-	val = __pmu_read_single(fd, &ts[0]);
-
-	ret = pipe2(link, O_NONBLOCK);
-	igt_assert_eq(ret, 0);
-
-	/*
-	 * Toggle online status of all the CPUs in a child process and ensure
-	 * this has not affected busyness stats in the parent.
-	 */
-	igt_fork(child, 1) {
-		int cpu = 0;
-
-		close(link[0]);
-
-		for (;;) {
-			char name[128];
-			int cpufd;
-
-			igt_assert_lt(snprintf(name, sizeof(name),
-					       "/sys/devices/system/cpu/cpu%d/online",
-					       cpu), sizeof(name));
-			cpufd = open(name, O_WRONLY);
-			if (cpufd == -1) {
-				igt_assert_lt(0, cpu);
-				/*
-				 * Signal parent that we cycled through all
-				 * CPUs and we are done.
-				 */
-				igt_assert_eq(write(link[1], "*", 1), 1);
-				break;
-			}
-
-			/* Offline followed by online a CPU. */
-
-			ret = write(cpufd, "0", 2);
-			if (ret < 0) {
-				/*
-				 * If we failed to offline a CPU we don't want
-				 * to proceed.
-				 */
-				igt_warn("Failed to offline cpu%u! (%d)\n",
-					 cpu, errno);
-				igt_assert_eq(write(link[1], "s", 1), 1);
-				break;
-			}
-
-			usleep(1e6);
-
-			ret = write(cpufd, "1", 2);
-			if (ret < 0) {
-				/*
-				 * Failed to bring a CPU back online is fatal
-				 * for the sanity of a test run so stop further
-				 * testing.
-				 */
-				igt_warn("Failed to online cpu%u! (%d)\n",
-					 cpu, errno);
-				igt_fatal_error();
-			}
-
-			close(cpufd);
-			cpu++;
-		}
-	}
-
-	close(link[1]);
-
-	/*
-	 * Very long batches can be declared as GPU hangs so emit shorter ones
-	 * until the CPU core shuffler finishes one loop.
-	 */
-	for (;;) {
-		usleep(500e3);
-		end_spin(gem_fd, spin[cur], 0);
-
-		/* Check if the child is signaling completion. */
-		ret = read(link[0], &buf, 1);
-		if ( ret == 1 || (ret < 0 && errno != EAGAIN))
-			break;
-
-		igt_spin_free(gem_fd, spin[cur]);
-		spin[cur] = __igt_spin_new(gem_fd, .ahnd = ahnd,
-					   .engine = I915_EXEC_DEFAULT);
-		cur ^= 1;
-	}
-
-	val = __pmu_read_single(fd, &ts[1]) - val;
-
-	end_spin(gem_fd, spin[0], FLAG_SYNC);
-	end_spin(gem_fd, spin[1], FLAG_SYNC);
-	igt_spin_free(gem_fd, spin[0]);
-	igt_spin_free(gem_fd, spin[1]);
-	igt_waitchildren();
-	close(fd);
-	close(link[0]);
-	put_ahnd(ahnd);
-
-	/* Skip if child signals a problem with offlining a CPU. */
-	igt_skip_on(buf == 's');
-
-	assert_within_epsilon(val, ts[1] - ts[0], tolerance);
-}
-
 static int target_num_interrupts(int i915)
 {
 	const intel_ctx_cfg_t cfg = intel_ctx_cfg_all_physical(i915);
@@ -2650,12 +2514,6 @@ igt_main
 		all_busy_check_all(fd, ctx, num_engines,
 				   TEST_BUSY | TEST_TRAILING_IDLE);
 
-	/**
-	 * Test counters are not affected by CPU offline/online events.
-	 */
-	igt_subtest("cpu-hotplug")
-		cpu_hotplug(fd);
-
 	/**
 	 * Test GPU frequency.
 	 */
-- 
2.48.0