[PATCH 3/3] sched_ext/scx_qmap: Add an example usage of DSQ iterator

Tejun Heo
2024-07-09T00:40:54Z

Implement periodic dumping of the shared DSQ to demonstrate the use of the
newly added DSQ iterator.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: David Vernet <dvernet@meta.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Cc: bpf@vger.kernel.org
---
tools/sched_ext/scx_qmap.bpf.c | 25 +++++++++++++++++++++++++
tools/sched_ext/scx_qmap.c | 8 ++++++--
2 files changed, 31 insertions(+), 2 deletions(-)

diff --git a/tools/sched_ext/scx_qmap.bpf.c b/tools/sched_ext/scx_qmap.bpf.c
index b1d0b09c966e..27e35066a602 100644
--- a/tools/sched_ext/scx_qmap.bpf.c
+++ b/tools/sched_ext/scx_qmap.bpf.c
@@ -36,6 +36,7 @@ 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 bool print_shared_dsq;
const volatile s32 disallow_tgid;
const volatile bool suppress_dump;

@@ -604,10 +605,34 @@ static void monitor_cpuperf(void)
scx_bpf_put_cpumask(online);
}

+/*
+ * Dump the currently queued tasks in the shared DSQ to demonstrate the usage of
+ * scx_bpf_dsq_nr_queued() and DSQ iterator. Raise the dispatch batch count to
+ * see meaningful dumps in the trace pipe.
+ */
+static void dump_shared_dsq(void)
+{
+ struct task_struct *p;
+ s32 nr;
+
+ if (!(nr = scx_bpf_dsq_nr_queued(SHARED_DSQ)))
+ return;
+
+ bpf_printk("Dumping %d tasks in SHARED_DSQ in reverse order", nr);
+
+ bpf_rcu_read_lock();
+ bpf_for_each(scx_dsq, p, SHARED_DSQ, SCX_DSQ_ITER_REV)
+ bpf_printk("%s[%d]", p->comm, p->pid);
+ bpf_rcu_read_unlock();
+}
+
static int monitor_timerfn(void *map, int *key, struct bpf_timer *timer)
{
monitor_cpuperf();

+ if (print_shared_dsq)
+ dump_shared_dsq();
+
bpf_timer_start(timer, ONE_SEC_IN_NS, 0);
return 0;
}
diff --git a/tools/sched_ext/scx_qmap.c b/tools/sched_ext/scx_qmap.c
index e4e3ecffc4cf..304f0488a386 100644
--- a/tools/sched_ext/scx_qmap.c
+++ b/tools/sched_ext/scx_qmap.c
@@ -20,7 +20,7 @@ const char help_fmt[] =
"See the top-level comment in .bpf.c for more details.\n"
"\n"
"Usage: %s [-s SLICE_US] [-e COUNT] [-t COUNT] [-T COUNT] [-l COUNT] [-b COUNT]\n"
-" [-d PID] [-D LEN] [-p] [-v]\n"
+" [-P] [-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"
@@ -28,6 +28,7 @@ const char help_fmt[] =
" -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"
+" -P Print out DSQ content to trace_pipe every second, use with -b\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"
" -S Suppress qmap-specific debug dump\n"
@@ -62,7 +63,7 @@ int main(int argc, char **argv)

skel = SCX_OPS_OPEN(qmap_ops, scx_qmap);

- while ((opt = getopt(argc, argv, "s:e:t:T:l:b:d:D:Spvh")) != -1) {
+ while ((opt = getopt(argc, argv, "s:e:t:T:l:b:Pd:D:Spvh")) != -1) {
switch (opt) {
case 's':
skel->rodata->slice_ns = strtoull(optarg, NULL, 0) * 1000;
@@ -82,6 +83,9 @@ int main(int argc, char **argv)
case 'b':
skel->rodata->dsp_batch = strtoul(optarg, NULL, 0);
break;
+ case 'P':
+ skel->rodata->print_shared_dsq = true;
+ break;
case 'd':
skel->rodata->disallow_tgid = strtol(optarg, NULL, 0);
if (skel->rodata->disallow_tgid < 0)
--
2.45.2