From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id EC618C2BB1D for ; Fri, 13 Mar 2020 17:47:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C2CC6206E2 for ; Fri, 13 Mar 2020 17:47:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727080AbgCMRrU (ORCPT ); Fri, 13 Mar 2020 13:47:20 -0400 Received: from Galois.linutronix.de ([193.142.43.55]:47702 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726477AbgCMRrR (ORCPT ); Fri, 13 Mar 2020 13:47:17 -0400 Received: from localhost ([127.0.0.1] helo=flow.W.breakpoint.cc) by Galois.linutronix.de with esmtp (Exim 4.80) (envelope-from ) id 1jCoOx-00017r-77; Fri, 13 Mar 2020 18:47:15 +0100 From: Sebastian Andrzej Siewior To: linux-kernel@vger.kernel.org Cc: Peter Zijlstra , Ingo Molnar , Will Deacon , "Paul E . McKenney" , Joel Fernandes , Steven Rostedt , Linus Torvalds , Thomas Gleixner , Sebastian Andrzej Siewior Subject: [PATCH 2/9] timekeeping: Split jiffies seqlock Date: Fri, 13 Mar 2020 18:46:54 +0100 Message-Id: <20200313174701.148376-3-bigeasy@linutronix.de> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20200313174701.148376-1-bigeasy@linutronix.de> References: <20200313174701.148376-1-bigeasy@linutronix.de> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Thomas Gleixner seqlock consists of a sequence counter and a spinlock_t which is used to serialize the writers. spinlock_t is substituted by a "sleeping" spinlock on PREEMPT_RT enabled kernels which breaks the usage in the timekeeping code as the writers are executed in hard interrupt and therefore non-preemptible context even on PREEMPT_RT. The spinlock in seqlock cannot be unconditionally replaced by a raw_spinlock_t as many seqlock users have nesting spinlock sections or other code which is not suitable to run in truly atomic context on RT. Instead of providing a raw_seqlock API for a single use case, open code the seqlock for the jiffies use case and implement it with a raw_spinlock_t and a sequence counter. Signed-off-by: Thomas Gleixner Signed-off-by: Sebastian Andrzej Siewior --- kernel/time/jiffies.c | 7 ++++--- kernel/time/tick-common.c | 10 ++++++---- kernel/time/tick-sched.c | 19 ++++++++++++------- kernel/time/timekeeping.c | 6 ++++-- kernel/time/timekeeping.h | 3 ++- 5 files changed, 28 insertions(+), 17 deletions(-) diff --git a/kernel/time/jiffies.c b/kernel/time/jiffies.c index d23b434c2ca7b..eddcf49704445 100644 --- a/kernel/time/jiffies.c +++ b/kernel/time/jiffies.c @@ -58,7 +58,8 @@ static struct clocksource clocksource_jiffies =3D { .max_cycles =3D 10, }; =20 -__cacheline_aligned_in_smp DEFINE_SEQLOCK(jiffies_lock); +__cacheline_aligned_in_smp DEFINE_RAW_SPINLOCK(jiffies_lock); +__cacheline_aligned_in_smp seqcount_t jiffies_seq; =20 #if (BITS_PER_LONG < 64) u64 get_jiffies_64(void) @@ -67,9 +68,9 @@ u64 get_jiffies_64(void) u64 ret; =20 do { - seq =3D read_seqbegin(&jiffies_lock); + seq =3D read_seqcount_begin(&jiffies_seq); ret =3D jiffies_64; - } while (read_seqretry(&jiffies_lock, seq)); + } while (read_seqcount_retry(&jiffies_seq, seq)); return ret; } EXPORT_SYMBOL(get_jiffies_64); diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c index 7e5d3524e924d..6c9c342dd0e53 100644 --- a/kernel/time/tick-common.c +++ b/kernel/time/tick-common.c @@ -84,13 +84,15 @@ int tick_is_oneshot_available(void) static void tick_periodic(int cpu) { if (tick_do_timer_cpu =3D=3D cpu) { - write_seqlock(&jiffies_lock); + raw_spin_lock(&jiffies_lock); + write_seqcount_begin(&jiffies_seq); =20 /* Keep track of the next tick event */ tick_next_period =3D ktime_add(tick_next_period, tick_period); =20 do_timer(1); - write_sequnlock(&jiffies_lock); + write_seqcount_end(&jiffies_seq); + raw_spin_unlock(&jiffies_lock); update_wall_time(); } =20 @@ -162,9 +164,9 @@ void tick_setup_periodic(struct clock_event_device *dev= , int broadcast) ktime_t next; =20 do { - seq =3D read_seqbegin(&jiffies_lock); + seq =3D read_seqcount_begin(&jiffies_seq); next =3D tick_next_period; - } while (read_seqretry(&jiffies_lock, seq)); + } while (read_seqcount_retry(&jiffies_seq, seq)); =20 clockevents_switch_state(dev, CLOCK_EVT_STATE_ONESHOT); =20 diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index a792d21cac645..4be756b88a48e 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -65,7 +65,8 @@ static void tick_do_update_jiffies64(ktime_t now) return; =20 /* Reevaluate with jiffies_lock held */ - write_seqlock(&jiffies_lock); + raw_spin_lock(&jiffies_lock); + write_seqcount_begin(&jiffies_seq); =20 delta =3D ktime_sub(now, last_jiffies_update); if (delta >=3D tick_period) { @@ -91,10 +92,12 @@ static void tick_do_update_jiffies64(ktime_t now) /* Keep the tick_next_period variable up to date */ tick_next_period =3D ktime_add(last_jiffies_update, tick_period); } else { - write_sequnlock(&jiffies_lock); + write_seqcount_end(&jiffies_seq); + raw_spin_unlock(&jiffies_lock); return; } - write_sequnlock(&jiffies_lock); + write_seqcount_end(&jiffies_seq); + raw_spin_unlock(&jiffies_lock); update_wall_time(); } =20 @@ -105,12 +108,14 @@ static ktime_t tick_init_jiffy_update(void) { ktime_t period; =20 - write_seqlock(&jiffies_lock); + raw_spin_lock(&jiffies_lock); + write_seqcount_begin(&jiffies_seq); /* Did we start the jiffies update yet ? */ if (last_jiffies_update =3D=3D 0) last_jiffies_update =3D tick_next_period; period =3D last_jiffies_update; - write_sequnlock(&jiffies_lock); + write_seqcount_end(&jiffies_seq); + raw_spin_unlock(&jiffies_lock); return period; } =20 @@ -676,10 +681,10 @@ static ktime_t tick_nohz_next_event(struct tick_sched= *ts, int cpu) =20 /* Read jiffies and the time when jiffies were updated last */ do { - seq =3D read_seqbegin(&jiffies_lock); + seq =3D read_seqcount_begin(&jiffies_seq); basemono =3D last_jiffies_update; basejiff =3D jiffies; - } while (read_seqretry(&jiffies_lock, seq)); + } while (read_seqcount_retry(&jiffies_seq, seq)); ts->last_jiffies =3D basejiff; ts->timer_expires_base =3D basemono; =20 diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index ca69290bee2a3..856280d2cbd4c 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -2397,8 +2397,10 @@ EXPORT_SYMBOL(hardpps); */ void xtime_update(unsigned long ticks) { - write_seqlock(&jiffies_lock); + raw_spin_lock(&jiffies_lock); + write_seqcount_begin(&jiffies_seq); do_timer(ticks); - write_sequnlock(&jiffies_lock); + write_seqcount_end(&jiffies_seq); + raw_spin_unlock(&jiffies_lock); update_wall_time(); } diff --git a/kernel/time/timekeeping.h b/kernel/time/timekeeping.h index 141ab3ab0354f..099737f6f10c7 100644 --- a/kernel/time/timekeeping.h +++ b/kernel/time/timekeeping.h @@ -25,7 +25,8 @@ static inline void sched_clock_resume(void) { } extern void do_timer(unsigned long ticks); extern void update_wall_time(void); =20 -extern seqlock_t jiffies_lock; +extern raw_spinlock_t jiffies_lock; +extern seqcount_t jiffies_seq; =20 #define CS_NAME_LEN 32 =20 --=20 2.25.1