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Sat, 31 Oct 2026 04:47:44 -0700 (PDT) Received: from scheduler.schedules ([85.100.66.184]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-48e71b728ddsm8374016f8f.9.2026.10.31.04.47.43 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 31 Oct 2026 04:47:44 -0700 (PDT) Date: Sat, 31 Oct 2026 14:47:41 +0300 From: Kayra Cizmeci To: Stian Halseth Cc: Frederic Weisbecker , Peter Zijlstra , Ingo Molnar , Linus Torvalds , Paul Menzel , Breno Leitao , Thorsten Leemhuis , Thomas Gleixner , Anna-Maria Behnsen , Shrikanth Hegde , regressions@lists.linux.dev, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] sched/cputime: Don't warn when the tick period starts after idle exit Message-ID: References: <20261031081408.3378884-1-stian@itx.no> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20261031081408.3378884-1-stian@itx.no> On Sat, Oct 31, 2026 at 09:14:07AM +0100, Stian Halseth wrote: > kernel/sched/cputime.c | 7 ++++++- > 1 file changed, 6 insertions(+), 1 deletion(-) > > diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c > index 9e0fb8633d823..17f3cbd5d403a 100644 > --- a/kernel/sched/cputime.c > +++ b/kernel/sched/cputime.c > @@ -478,7 +478,12 @@ void kcpustat_dyntick_stop(u64 now, u64 tick_start) > kc->idle_tick_overlap = 0; > } > tick_start = max(tick_start, kc->idle_dyntick_entry); > - if (!WARN_ON_ONCE(now < tick_start)) > + /* > + * After a switch from the jiffies clocksource the tick can be > + * armed more than a tick ahead, so the period may not have > + * started yet. > + */ > + if (now > tick_start) > kc->idle_tick_overlap += now - tick_start; > kcpustat_idle_stop(kc, now); > kc->idle_dyntick = false; > -- > 2.43.0 TICK_NSEC = 4 switch | v Real: 8 9 10 11 12 13 14 15 16 17 18 Time: 8 8 8 9 10 11 12 13 14 15 16 Tick: 8 8 8 8 10 10 10 10 10 10 16 So if we enter idle at real-12, and exit at real-13 this happens: last_tick is 16, so last_tick - 4 = 12. But normally, last_tick needs to be 14 and tick_start needs to be 10. Or am I missing something? IDK if there is a better solution tho. Maybe fixing it from the root would be better. If its even possible to do it cleanly... But this code works correct. Reviewed-by: Kayra Cizmeci Thanks, Kayra