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From:   Chris Metcalf <cmetcalf@mellanox.com>
To:     Steven Rostedt <rostedt@goodmis.org>,
        Ingo Molnar <mingo@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Rik van Riel <riel@redhat.com>, Tejun Heo <tj@kernel.org>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Christoph Lameter <cl@linux.com>,
        Viresh Kumar <viresh.kumar@linaro.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will.deacon@arm.com>,
        Andy Lutomirski <luto@amacapital.net>,
        Michal Hocko <mhocko@suse.com>, linux-kernel@vger.kernel.org
Cc:     Chris Metcalf <cmetcalf@mellanox.com>
Subject: [PATCH v16 05/13] Add try_stop_full_tick() API for NO_HZ_FULL
Date:   Fri,  3 Nov 2017 13:04:44 -0400
Message-Id: <1509728692-10460-6-git-send-email-cmetcalf@mellanox.com>
In-Reply-To: <1509728692-10460-1-git-send-email-cmetcalf@mellanox.com>
References: <1509728692-10460-1-git-send-email-cmetcalf@mellanox.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

This API checks to see if the scheduler tick can be stopped,
and if so, stops it and returns 0; otherwise it returns an error.
This is intended for use with task isolation, where we will want to
be able to stop the tick synchronously when returning to userspace.

Signed-off-by: Chris Metcalf <cmetcalf@mellanox.com>
---
 include/linux/tick.h     |  1 +
 kernel/time/tick-sched.c | 18 ++++++++++++++++++
 2 files changed, 19 insertions(+)

diff --git a/include/linux/tick.h b/include/linux/tick.h
index fe01e68bf520..078ff2464b00 100644
--- a/include/linux/tick.h
+++ b/include/linux/tick.h
@@ -234,6 +234,7 @@ static inline void tick_dep_clear_signal(struct signal_struct *signal,
 
 extern void tick_nohz_full_kick_cpu(int cpu);
 extern void __tick_nohz_task_switch(void);
+extern int try_stop_full_tick(void);
 #else
 static inline int housekeeping_any_cpu(void)
 {
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index c7a899c5ce64..c026145eba2f 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -861,6 +861,24 @@ static void tick_nohz_full_update_tick(struct tick_sched *ts)
 #endif
 }
 
+#ifdef CONFIG_TASK_ISOLATION
+int try_stop_full_tick(void)
+{
+	int cpu = smp_processor_id();
+	struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
+
+	/* For an unstable clock, we should return a permanent error code. */
+	if (atomic_read(&tick_dep_mask) & TICK_DEP_MASK_CLOCK_UNSTABLE)
+		return -EINVAL;
+
+	if (!can_stop_full_tick(cpu, ts))
+		return -EAGAIN;
+
+	tick_nohz_stop_sched_tick(ts, ktime_get(), cpu);
+	return 0;
+}
+#endif
+
 static bool can_stop_idle_tick(int cpu, struct tick_sched *ts)
 {
 	/*
-- 
2.1.2


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