Messages in this thread | | | Date | Wed, 7 Jul 2021 12:43:53 +0200 | From | Frederic Weisbecker <> | Subject | Re: [PATCH v1] Add info log when user enables NOHZ in commandline but NOHZ is not possible |
| |
On Wed, Jul 07, 2021 at 12:16:15PM +0200, Thomas Gleixner wrote: > Ani, > > On Sun, Jun 27 2021 at 12:58, Ani Sinha wrote: > > same comment vs. Subject, 'this patch' and 'we' > > > @@ -930,6 +930,7 @@ static void tick_nohz_full_update_tick(struct tick_sched *ts) > > { > > #ifdef CONFIG_NO_HZ_FULL > > int cpu = smp_processor_id(); > > + static bool no_tick_warned; > > > > if (!tick_nohz_full_cpu(cpu)) > > return; > > @@ -937,10 +938,24 @@ static void tick_nohz_full_update_tick(struct tick_sched *ts) > > if (!ts->tick_stopped && ts->nohz_mode == NOHZ_MODE_INACTIVE) > > return; > > > > - if (can_stop_full_tick(cpu, ts)) > > + if (can_stop_full_tick(cpu, ts)) { > > tick_nohz_stop_sched_tick(ts, cpu); > > - else if (ts->tick_stopped) > > - tick_nohz_restart_sched_tick(ts, ktime_get()); > > + if (no_tick_warned) { > > + pr_info("NO_HZ_FULL is now enabled in the system.\n"); > > + no_tick_warned = false; > > + } > > + } else { > > + /* > > + * Don't allow the user to think they can get > > + * full NO_HZ with this machine. > > + */ > > + if (!no_tick_warned && tick_nohz_full_running) { > > + pr_info("NO_HZ_FULL has been disabled in the system."); > > + no_tick_warned = true; > > + } > > So this is going to emit this message everytime the NOHZ state of a CPU > changes, which is an easy to trigger dmesg flooding from unpriviledged > user space. > > Also the message is misleading because this is a per CPU condition and > not a system wide condition.
IIUC, the clock can be marked unstable anytime before or after nohz_full is initialized.
So we can do two things:
* If tick_nohz_init() is called after the clock has been marked unstable, just don't initialize nohz_full.
* If the clock is marked unstable after tick_nohz_init(), issue a pr_warn() from __clear_sched_clock_stable().
Thanks.
| |