2 files changed, 21 insertions, 2 deletions

diff --git a/tools/sched_ext/scx_qmap.bpf.c b/tools/sched_ext/scx_qmap.bpf.c
index 5b3da28bf0429..879fc9c788e55 100644
--- a/tools/sched_ext/scx_qmap.bpf.c
+++ b/tools/sched_ext/scx_qmap.bpf.c
@@ -31,6 +31,7 @@ char _license[] SEC("license") = "GPL";
 const volatile u64 slice_ns = SCX_SLICE_DFL;
 const volatile u32 stall_user_nth;
 const volatile u32 stall_kernel_nth;
+const volatile u32 dsp_inf_loop_after;
 const volatile u32 dsp_batch;
 const volatile s32 disallow_tgid;
 const volatile bool suppress_dump;
@@ -198,6 +199,20 @@ void BPF_STRUCT_OPS(qmap_dispatch, s32 cpu, struct task_struct *prev)
 	if (scx_bpf_consume(SHARED_DSQ))
 		return;
 
+	if (dsp_inf_loop_after && nr_dispatched > dsp_inf_loop_after) {
+		/*
+		 * PID 2 should be kthreadd which should mostly be idle and off
+		 * the scheduler. Let's keep dispatching it to force the kernel
+		 * to call this function over and over again.
+		 */
+		p = bpf_task_from_pid(2);
+		if (p) {
+			scx_bpf_dispatch(p, SCX_DSQ_LOCAL, slice_ns, 0);
+			bpf_task_release(p);
+			return;
+		}
+	}
+
 	if (!(cpuc = bpf_map_lookup_elem(&cpu_ctx_stor, &zero))) {
 		scx_bpf_error("failed to look up cpu_ctx");
 		return;
diff --git a/tools/sched_ext/scx_qmap.c b/tools/sched_ext/scx_qmap.c
index a1123a17581b3..594147a710a85 100644
--- a/tools/sched_ext/scx_qmap.c
+++ b/tools/sched_ext/scx_qmap.c
@@ -19,13 +19,14 @@ const char help_fmt[] =
 "\n"
 "See the top-level comment in .bpf.c for more details.\n"
 "\n"
-"Usage: %s [-s SLICE_US] [-e COUNT] [-t COUNT] [-T COUNT] [-b COUNT]\n"
+"Usage: %s [-s SLICE_US] [-e COUNT] [-t COUNT] [-T COUNT] [-l COUNT] [-b COUNT]\n"
 "       [-d PID] [-D LEN] [-p] [-v]\n"
 "\n"
 "  -s SLICE_US   Override slice duration\n"
 "  -e COUNT      Trigger scx_bpf_error() after COUNT enqueues\n"
 "  -t COUNT      Stall every COUNT'th user thread\n"
 "  -T COUNT      Stall every COUNT'th kernel thread\n"
+"  -l COUNT      Trigger dispatch infinite looping after COUNT dispatches\n"
 "  -b COUNT      Dispatch upto COUNT tasks together\n"
 "  -d PID        Disallow a process from switching into SCHED_EXT (-1 for self)\n"
 "  -D LEN        Set scx_exit_info.dump buffer length\n"
@@ -61,7 +62,7 @@ int main(int argc, char **argv)
 
 	skel = SCX_OPS_OPEN(qmap_ops, scx_qmap);
 
-	while ((opt = getopt(argc, argv, "s:e:t:T:b:d:D:Spvh")) != -1) {
+	while ((opt = getopt(argc, argv, "s:e:t:T:l:b:d:D:Spvh")) != -1) {
 		switch (opt) {
 		case 's':
 			skel->rodata->slice_ns = strtoull(optarg, NULL, 0) * 1000;
@@ -75,6 +76,9 @@ int main(int argc, char **argv)
 		case 'T':
 			skel->rodata->stall_kernel_nth = strtoul(optarg, NULL, 0);
 			break;
+		case 'l':
+			skel->rodata->dsp_inf_loop_after = strtoul(optarg, NULL, 0);
+			break;
 		case 'b':
 			skel->rodata->dsp_batch = strtoul(optarg, NULL, 0);
 			break;