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Message-ID: <aNJWGrp08ucA4Ov2@gpd4>
Date: Tue, 23 Sep 2025 10:11:06 +0200
From: Andrea Righi <arighi@...dia.com>
To: Tejun Heo <tj@...nel.org>
Cc: David Vernet <void@...ifault.com>, Changwoo Min <changwoo@...lia.com>,
linux-kernel@...r.kernel.org, sched-ext@...ts.linux.dev
Subject: Re: [PATCH 7/7] tools/sched_ext: scx_qmap: Make debug output quieter
by default
On Sun, Sep 21, 2025 at 03:32:46PM -1000, Tejun Heo wrote:
> scx_qmap currently outputs verbose debug messages including cgroup operations
> and CPU online/offline events by default, which can be noisy during normal
> operation. While the existing -P option controls DSQ dumps and event
> statistics, there's no way to suppress the other debug messages.
>
> Split the debug output controls to make scx_qmap quieter by default. The -P
> option continues to control DSQ dumps and event statistics
> (print_dsqs_and_events), while a new -M option controls debug messages like
> cgroup operations and CPU events (print_msgs). This allows users to run
> scx_qmap with minimal output and selectively enable debug information as
> needed.
>
> Signed-off-by: Tejun Heo <tj@...nel.org>
Acked-by: Andrea Righi <arighi@...dia.com>
Thanks,
-Andrea
> ---
> tools/sched_ext/scx_qmap.bpf.c | 80 +++++++++++++++++++---------------
> tools/sched_ext/scx_qmap.c | 12 +++--
> 2 files changed, 53 insertions(+), 39 deletions(-)
>
> diff --git a/tools/sched_ext/scx_qmap.bpf.c b/tools/sched_ext/scx_qmap.bpf.c
> index cd50a94326e3..3072b593f898 100644
> --- a/tools/sched_ext/scx_qmap.bpf.c
> +++ b/tools/sched_ext/scx_qmap.bpf.c
> @@ -39,7 +39,8 @@ const volatile u32 stall_kernel_nth;
> const volatile u32 dsp_inf_loop_after;
> const volatile u32 dsp_batch;
> const volatile bool highpri_boosting;
> -const volatile bool print_shared_dsq;
> +const volatile bool print_dsqs_and_events;
> +const volatile bool print_msgs;
> const volatile s32 disallow_tgid;
> const volatile bool suppress_dump;
>
> @@ -633,22 +634,25 @@ void BPF_STRUCT_OPS(qmap_dump_task, struct scx_dump_ctx *dctx, struct task_struc
>
> s32 BPF_STRUCT_OPS(qmap_cgroup_init, struct cgroup *cgrp, struct scx_cgroup_init_args *args)
> {
> - bpf_printk("CGRP INIT %llu weight=%u period=%lu quota=%ld burst=%lu",
> - cgrp->kn->id, args->weight, args->bw_period_us,
> - args->bw_quota_us, args->bw_burst_us);
> + if (print_msgs)
> + bpf_printk("CGRP INIT %llu weight=%u period=%lu quota=%ld burst=%lu",
> + cgrp->kn->id, args->weight, args->bw_period_us,
> + args->bw_quota_us, args->bw_burst_us);
> return 0;
> }
>
> void BPF_STRUCT_OPS(qmap_cgroup_set_weight, struct cgroup *cgrp, u32 weight)
> {
> - bpf_printk("CGRP SET %llu weight=%u", cgrp->kn->id, weight);
> + if (print_msgs)
> + bpf_printk("CGRP SET %llu weight=%u", cgrp->kn->id, weight);
> }
>
> void BPF_STRUCT_OPS(qmap_cgroup_set_bandwidth, struct cgroup *cgrp,
> u64 period_us, u64 quota_us, u64 burst_us)
> {
> - bpf_printk("CGRP SET %llu period=%lu quota=%ld burst=%lu", cgrp->kn->id,
> - period_us, quota_us, burst_us);
> + if (print_msgs)
> + bpf_printk("CGRP SET %llu period=%lu quota=%ld burst=%lu",
> + cgrp->kn->id, period_us, quota_us, burst_us);
> }
>
> /*
> @@ -692,16 +696,20 @@ static void print_cpus(void)
>
> void BPF_STRUCT_OPS(qmap_cpu_online, s32 cpu)
> {
> - bpf_printk("CPU %d coming online", cpu);
> - /* @cpu is already online at this point */
> - print_cpus();
> + if (print_msgs) {
> + bpf_printk("CPU %d coming online", cpu);
> + /* @cpu is already online at this point */
> + print_cpus();
> + }
> }
>
> void BPF_STRUCT_OPS(qmap_cpu_offline, s32 cpu)
> {
> - bpf_printk("CPU %d going offline", cpu);
> - /* @cpu is still online at this point */
> - print_cpus();
> + if (print_msgs) {
> + bpf_printk("CPU %d going offline", cpu);
> + /* @cpu is still online at this point */
> + print_cpus();
> + }
> }
>
> struct monitor_timer {
> @@ -799,35 +807,36 @@ static void dump_shared_dsq(void)
>
> static int monitor_timerfn(void *map, int *key, struct bpf_timer *timer)
> {
> - struct scx_event_stats events;
> -
> bpf_rcu_read_lock();
> dispatch_highpri(true);
> bpf_rcu_read_unlock();
>
> monitor_cpuperf();
>
> - if (print_shared_dsq)
> + if (print_dsqs_and_events) {
> + struct scx_event_stats events;
> +
> dump_shared_dsq();
>
> - __COMPAT_scx_bpf_events(&events, sizeof(events));
> -
> - bpf_printk("%35s: %lld", "SCX_EV_SELECT_CPU_FALLBACK",
> - scx_read_event(&events, SCX_EV_SELECT_CPU_FALLBACK));
> - bpf_printk("%35s: %lld", "SCX_EV_DISPATCH_LOCAL_DSQ_OFFLINE",
> - scx_read_event(&events, SCX_EV_DISPATCH_LOCAL_DSQ_OFFLINE));
> - bpf_printk("%35s: %lld", "SCX_EV_DISPATCH_KEEP_LAST",
> - scx_read_event(&events, SCX_EV_DISPATCH_KEEP_LAST));
> - bpf_printk("%35s: %lld", "SCX_EV_ENQ_SKIP_EXITING",
> - scx_read_event(&events, SCX_EV_ENQ_SKIP_EXITING));
> - bpf_printk("%35s: %lld", "SCX_EV_REFILL_SLICE_DFL",
> - scx_read_event(&events, SCX_EV_REFILL_SLICE_DFL));
> - bpf_printk("%35s: %lld", "SCX_EV_BYPASS_DURATION",
> - scx_read_event(&events, SCX_EV_BYPASS_DURATION));
> - bpf_printk("%35s: %lld", "SCX_EV_BYPASS_DISPATCH",
> - scx_read_event(&events, SCX_EV_BYPASS_DISPATCH));
> - bpf_printk("%35s: %lld", "SCX_EV_BYPASS_ACTIVATE",
> - scx_read_event(&events, SCX_EV_BYPASS_ACTIVATE));
> + __COMPAT_scx_bpf_events(&events, sizeof(events));
> +
> + bpf_printk("%35s: %lld", "SCX_EV_SELECT_CPU_FALLBACK",
> + scx_read_event(&events, SCX_EV_SELECT_CPU_FALLBACK));
> + bpf_printk("%35s: %lld", "SCX_EV_DISPATCH_LOCAL_DSQ_OFFLINE",
> + scx_read_event(&events, SCX_EV_DISPATCH_LOCAL_DSQ_OFFLINE));
> + bpf_printk("%35s: %lld", "SCX_EV_DISPATCH_KEEP_LAST",
> + scx_read_event(&events, SCX_EV_DISPATCH_KEEP_LAST));
> + bpf_printk("%35s: %lld", "SCX_EV_ENQ_SKIP_EXITING",
> + scx_read_event(&events, SCX_EV_ENQ_SKIP_EXITING));
> + bpf_printk("%35s: %lld", "SCX_EV_REFILL_SLICE_DFL",
> + scx_read_event(&events, SCX_EV_REFILL_SLICE_DFL));
> + bpf_printk("%35s: %lld", "SCX_EV_BYPASS_DURATION",
> + scx_read_event(&events, SCX_EV_BYPASS_DURATION));
> + bpf_printk("%35s: %lld", "SCX_EV_BYPASS_DISPATCH",
> + scx_read_event(&events, SCX_EV_BYPASS_DISPATCH));
> + bpf_printk("%35s: %lld", "SCX_EV_BYPASS_ACTIVATE",
> + scx_read_event(&events, SCX_EV_BYPASS_ACTIVATE));
> + }
>
> bpf_timer_start(timer, ONE_SEC_IN_NS, 0);
> return 0;
> @@ -839,7 +848,8 @@ s32 BPF_STRUCT_OPS_SLEEPABLE(qmap_init)
> struct bpf_timer *timer;
> s32 ret;
>
> - print_cpus();
> + if (print_msgs)
> + print_cpus();
>
> ret = scx_bpf_create_dsq(SHARED_DSQ, -1);
> if (ret)
> diff --git a/tools/sched_ext/scx_qmap.c b/tools/sched_ext/scx_qmap.c
> index c4912ab2e76f..ef701d45ba43 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"
> -" [-P] [-d PID] [-D LEN] [-p] [-v]\n"
> +" [-P] [-M] [-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"
> @@ -28,7 +28,8 @@ 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"
> +" -P Print out DSQ content and event counters to trace_pipe every second\n"
> +" -M Print out debug messages to trace_pipe\n"
> " -H Boost nice -20 tasks in SHARED_DSQ, 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"
> @@ -66,7 +67,7 @@ int main(int argc, char **argv)
>
> skel->rodata->slice_ns = __COMPAT_ENUM_OR_ZERO("scx_public_consts", "SCX_SLICE_DFL");
>
> - while ((opt = getopt(argc, argv, "s:e:t:T:l:b:PHd:D:Spvh")) != -1) {
> + while ((opt = getopt(argc, argv, "s:e:t:T:l:b:PMHd:D:Spvh")) != -1) {
> switch (opt) {
> case 's':
> skel->rodata->slice_ns = strtoull(optarg, NULL, 0) * 1000;
> @@ -87,7 +88,10 @@ int main(int argc, char **argv)
> skel->rodata->dsp_batch = strtoul(optarg, NULL, 0);
> break;
> case 'P':
> - skel->rodata->print_shared_dsq = true;
> + skel->rodata->print_dsqs_and_events = true;
> + break;
> + case 'M':
> + skel->rodata->print_msgs = true;
> break;
> case 'H':
> skel->rodata->highpri_boosting = true;
> --
> 2.51.0
>
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