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Cc: Gusenleitner Klaus <gus@keba.com>, Sebastian Andrzej Siewior <bigeasy@linutronix.de>, Thomas Gleixner <tglx@linutronix.de>, x86@kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <20230406095735.0_14edn3@linutronix.de> References: <20230406095735.0_14edn3@linutronix.de> MIME-Version: 1.0 Message-ID: <168182364782.404.4164105102665678709.tip-bot2@tip-bot2> Robot-ID: <tip-bot2@linutronix.de> Robot-Unsubscribe: Contact <mailto:tglx@linutronix.de> to get blacklisted from these emails Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-Spam-Status: No, score=-4.4 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_MED,SPF_HELO_NONE, SPF_PASS,T_SCC_BODY_TEXT_LINE,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: <linux-kernel.vger.kernel.org> X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1763523408125578125?= X-GMAIL-MSGID: =?utf-8?q?1763523408125578125?= |
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[tip:,timers/core] tick/common: Align tick period with the HZ tick.
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Commit Message
tip-bot2 for Thomas Gleixner
April 18, 2023, 1:14 p.m. UTC
The following commit has been merged into the timers/core branch of tip: Commit-ID: e9523a0d81899361214d118ad60ef76f0e92f71d Gitweb: https://git.kernel.org/tip/e9523a0d81899361214d118ad60ef76f0e92f71d Author: Sebastian Andrzej Siewior <bigeasy@linutronix.de> AuthorDate: Tue, 18 Apr 2023 14:26:39 +02:00 Committer: Thomas Gleixner <tglx@linutronix.de> CommitterDate: Tue, 18 Apr 2023 15:06:50 +02:00 tick/common: Align tick period with the HZ tick. With HIGHRES enabled tick_sched_timer() is programmed every jiffy to expire the timer_list timers. This timer is programmed accurate in respect to CLOCK_MONOTONIC so that 0 seconds and nanoseconds is the first tick and the next one is 1000/CONFIG_HZ ms later. For HZ=250 it is every 4 ms and so based on the current time the next tick can be computed. This accuracy broke since the commit mentioned below because the jiffy based clocksource is initialized with higher accuracy in read_persistent_wall_and_boot_offset(). This higher accuracy is inherited during the setup in tick_setup_device(). The timer still fires every 4ms with HZ=250 but timer is no longer aligned with CLOCK_MONOTONIC with 0 as it origin but has an offset in the us/ns part of the timestamp. The offset differs with every boot and makes it impossible for user land to align with the tick. Align the tick period with CLOCK_MONOTONIC ensuring that it is always a multiple of 1000/CONFIG_HZ ms. Fixes: 857baa87b6422 ("sched/clock: Enable sched clock early") Reported-by: Gusenleitner Klaus <gus@keba.com> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Link: https://lore.kernel.org/20230406095735.0_14edn3@linutronix.de Link: https://lore.kernel.org/r/20230418122639.ikgfvu3f@linutronix.de --- kernel/time/tick-common.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-)
diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c index 4678935..65b8658 100644 --- a/kernel/time/tick-common.c +++ b/kernel/time/tick-common.c @@ -218,9 +218,19 @@ static void tick_setup_device(struct tick_device *td, * this cpu: */ if (tick_do_timer_cpu == TICK_DO_TIMER_BOOT) { + ktime_t next_p; + u32 rem; + tick_do_timer_cpu = cpu; - tick_next_period = ktime_get(); + next_p = ktime_get(); + div_u64_rem(next_p, TICK_NSEC, &rem); + if (rem) { + next_p -= rem; + next_p += TICK_NSEC; + } + + tick_next_period = next_p; #ifdef CONFIG_NO_HZ_FULL /* * The boot CPU may be nohz_full, in which case set