sched/nohz: Rewrite and fix load-avg computation -- again (5167e8d5) · Commits · 戴 / test

include/linux/sched.h

+8 −0

Original line number	Original line	Diff line number	Diff line
	@@ -1909,6 +1909,14 @@ static inline int set_cpus_allowed_ptr(struct task_struct *p,
	}		}
	#endif		#endif

			#ifdef CONFIG_NO_HZ
			void calc_load_enter_idle(void);
			void calc_load_exit_idle(void);
			#else
			static inline void calc_load_enter_idle(void) { }
			static inline void calc_load_exit_idle(void) { }
			#endif /* CONFIG_NO_HZ */

	#ifndef CONFIG_CPUMASK_OFFSTACK		#ifndef CONFIG_CPUMASK_OFFSTACK
	static inline int set_cpus_allowed(struct task_struct *p, cpumask_t new_mask)		static inline int set_cpus_allowed(struct task_struct *p, cpumask_t new_mask)
	{		{

kernel/sched/core.c

+203 −72

Original line number	Original line	Diff line number	Diff line
	@@ -2161,11 +2161,73 @@ unsigned long this_cpu_load(void)
	}		}


			/*
			* Global load-average calculations
			*
			* We take a distributed and async approach to calculating the global load-avg
			* in order to minimize overhead.
			*
			* The global load average is an exponentially decaying average of nr_running +
			* nr_uninterruptible.
			*
			* Once every LOAD_FREQ:
			*
			* nr_active = 0;
			* for_each_possible_cpu(cpu)
			* nr_active += cpu_of(cpu)->nr_running + cpu_of(cpu)->nr_uninterruptible;
			*
			* avenrun[n] = avenrun[0] * exp_n + nr_active * (1 - exp_n)
			*
			* Due to a number of reasons the above turns in the mess below:
			*
			* - for_each_possible_cpu() is prohibitively expensive on machines with
			* serious number of cpus, therefore we need to take a distributed approach
			* to calculating nr_active.
			*
			* \Sum_i x_i(t) = \Sum_i x_i(t) - x_i(t_0) \| x_i(t_0) := 0
			* = \Sum_i { \Sum_j=1 x_i(t_j) - x_i(t_j-1) }
			*
			* So assuming nr_active := 0 when we start out -- true per definition, we
			* can simply take per-cpu deltas and fold those into a global accumulate
			* to obtain the same result. See calc_load_fold_active().
			*
			* Furthermore, in order to avoid synchronizing all per-cpu delta folding
			* across the machine, we assume 10 ticks is sufficient time for every
			* cpu to have completed this task.
			*
			* This places an upper-bound on the IRQ-off latency of the machine. Then
			* again, being late doesn't loose the delta, just wrecks the sample.
			*
			* - cpu_rq()->nr_uninterruptible isn't accurately tracked per-cpu because
			* this would add another cross-cpu cacheline miss and atomic operation
			* to the wakeup path. Instead we increment on whatever cpu the task ran
			* when it went into uninterruptible state and decrement on whatever cpu
			* did the wakeup. This means that only the sum of nr_uninterruptible over
			* all cpus yields the correct result.
			*
			* This covers the NO_HZ=n code, for extra head-aches, see the comment below.
			*/

	/* Variables and functions for calc_load */		/* Variables and functions for calc_load */
	static atomic_long_t calc_load_tasks;		static atomic_long_t calc_load_tasks;
	static unsigned long calc_load_update;		static unsigned long calc_load_update;
	unsigned long avenrun[3];		unsigned long avenrun[3];
	EXPORT_SYMBOL(avenrun);		EXPORT_SYMBOL(avenrun); /* should be removed */

			/**
			* get_avenrun - get the load average array
			* @loads: pointer to dest load array
			* @offset: offset to add
			* @shift: shift count to shift the result left
			*
			* These values are estimates at best, so no need for locking.
			*/
			void get_avenrun(unsigned long *loads, unsigned long offset, int shift)
			{
			loads[0] = (avenrun[0] + offset) << shift;
			loads[1] = (avenrun[1] + offset) << shift;
			loads[2] = (avenrun[2] + offset) << shift;
			}

	static long calc_load_fold_active(struct rq *this_rq)		static long calc_load_fold_active(struct rq *this_rq)
	{		{
	@@ -2182,6 +2244,9 @@ static long calc_load_fold_active(struct rq *this_rq)
	return delta;		return delta;
	}		}

			/*
			* a1 = a0 * e + a * (1 - e)
			*/
	static unsigned long		static unsigned long
	calc_load(unsigned long load, unsigned long exp, unsigned long active)		calc_load(unsigned long load, unsigned long exp, unsigned long active)
	{		{
	@@ -2193,30 +2258,118 @@ calc_load(unsigned long load, unsigned long exp, unsigned long active)

	#ifdef CONFIG_NO_HZ		#ifdef CONFIG_NO_HZ
	/*		/*
	* For NO_HZ we delay the active fold to the next LOAD_FREQ update.		* Handle NO_HZ for the global load-average.
			*
			* Since the above described distributed algorithm to compute the global
			* load-average relies on per-cpu sampling from the tick, it is affected by
			* NO_HZ.
			*
			* The basic idea is to fold the nr_active delta into a global idle-delta upon
			* entering NO_HZ state such that we can include this as an 'extra' cpu delta
			* when we read the global state.
			*
			* Obviously reality has to ruin such a delightfully simple scheme:
			*
			* - When we go NO_HZ idle during the window, we can negate our sample
			* contribution, causing under-accounting.
			*
			* We avoid this by keeping two idle-delta counters and flipping them
			* when the window starts, thus separating old and new NO_HZ load.
			*
			* The only trick is the slight shift in index flip for read vs write.
			*
			* 0s 5s 10s 15s
			* +10 +10 +10 +10
			* \|-\|-----------\|-\|-----------\|-\|-----------\|-\|
			* r:0 0 1 1 0 0 1 1 0
			* w:0 1 1 0 0 1 1 0 0
			*
			* This ensures we'll fold the old idle contribution in this window while
			* accumlating the new one.
			*
			* - When we wake up from NO_HZ idle during the window, we push up our
			* contribution, since we effectively move our sample point to a known
			* busy state.
			*
			* This is solved by pushing the window forward, and thus skipping the
			* sample, for this cpu (effectively using the idle-delta for this cpu which
			* was in effect at the time the window opened). This also solves the issue
			* of having to deal with a cpu having been in NOHZ idle for multiple
			* LOAD_FREQ intervals.
	*		*
	* When making the ILB scale, we should try to pull this in as well.		* When making the ILB scale, we should try to pull this in as well.
	*/		*/
	static atomic_long_t calc_load_tasks_idle;		static atomic_long_t calc_load_idle[2];
			static int calc_load_idx;

			static inline int calc_load_write_idx(void)
			{
			int idx = calc_load_idx;

			/*
			* See calc_global_nohz(), if we observe the new index, we also
			* need to observe the new update time.
			*/
			smp_rmb();

			/*
			* If the folding window started, make sure we start writing in the
			* next idle-delta.
			*/
			if (!time_before(jiffies, calc_load_update))
			idx++;

			return idx & 1;
			}

			static inline int calc_load_read_idx(void)
			{
			return calc_load_idx & 1;
			}

	void calc_load_account_idle(struct rq *this_rq)		void calc_load_enter_idle(void)
	{		{
			struct rq *this_rq = this_rq();
	long delta;		long delta;

			/*
			* We're going into NOHZ mode, if there's any pending delta, fold it
			* into the pending idle delta.
			*/
	delta = calc_load_fold_active(this_rq);		delta = calc_load_fold_active(this_rq);
	if (delta)		if (delta) {
	atomic_long_add(delta, &calc_load_tasks_idle);		int idx = calc_load_write_idx();
			atomic_long_add(delta, &calc_load_idle[idx]);
			}
	}		}

	static long calc_load_fold_idle(void)		void calc_load_exit_idle(void)
	{		{
	long delta = 0;		struct rq *this_rq = this_rq();

			/*
			* If we're still before the sample window, we're done.
			*/
			if (time_before(jiffies, this_rq->calc_load_update))
			return;

	/*		/*
	* Its got a race, we don't care...		* We woke inside or after the sample window, this means we're already
			* accounted through the nohz accounting, so skip the entire deal and
			* sync up for the next window.
	*/		*/
	if (atomic_long_read(&calc_load_tasks_idle))		this_rq->calc_load_update = calc_load_update;
	delta = atomic_long_xchg(&calc_load_tasks_idle, 0);		if (time_before(jiffies, this_rq->calc_load_update + 10))
			this_rq->calc_load_update += LOAD_FREQ;
			}

			static long calc_load_fold_idle(void)
			{
			int idx = calc_load_read_idx();
			long delta = 0;

			if (atomic_long_read(&calc_load_idle[idx]))
			delta = atomic_long_xchg(&calc_load_idle[idx], 0);

	return delta;		return delta;
	}		}
	@@ -2302,22 +2455,7 @@ static void calc_global_nohz(void)
	{		{
	long delta, active, n;		long delta, active, n;

	/*		if (!time_before(jiffies, calc_load_update + 10)) {
	* If we crossed a calc_load_update boundary, make sure to fold
	* any pending idle changes, the respective CPUs might have
	* missed the tick driven calc_load_account_active() update
	* due to NO_HZ.
	*/
	delta = calc_load_fold_idle();
	if (delta)
	atomic_long_add(delta, &calc_load_tasks);

	/*
	* It could be the one fold was all it took, we done!
	*/
	if (time_before(jiffies, calc_load_update + 10))
	return;

	/*		/*
	* Catch-up, fold however many we are behind still		* Catch-up, fold however many we are behind still
	*/		*/
	@@ -2333,35 +2471,23 @@ static void calc_global_nohz(void)

	calc_load_update += n * LOAD_FREQ;		calc_load_update += n * LOAD_FREQ;
	}		}
	#else
	void calc_load_account_idle(struct rq *this_rq)
	{
	}

	static inline long calc_load_fold_idle(void)
	{
	return 0;
	}

	static void calc_global_nohz(void)		/*
	{		* Flip the idle index...
	}
	#endif

	/**
	* get_avenrun - get the load average array
	* @loads: pointer to dest load array
	* @offset: offset to add
	* @shift: shift count to shift the result left
	*		*
	* These values are estimates at best, so no need for locking.		* Make sure we first write the new time then flip the index, so that
			* calc_load_write_idx() will see the new time when it reads the new
			* index, this avoids a double flip messing things up.
	*/		*/
	void get_avenrun(unsigned long *loads, unsigned long offset, int shift)		smp_wmb();
	{		calc_load_idx++;
	loads[0] = (avenrun[0] + offset) << shift;
	loads[1] = (avenrun[1] + offset) << shift;
	loads[2] = (avenrun[2] + offset) << shift;
	}		}
			#else /* !CONFIG_NO_HZ */

			static inline long calc_load_fold_idle(void) { return 0; }
			static inline void calc_global_nohz(void) { }

			#endif /* CONFIG_NO_HZ */

	/*		/*
	* calc_load - update the avenrun load estimates 10 ticks after the		* calc_load - update the avenrun load estimates 10 ticks after the
	@@ -2369,11 +2495,18 @@ void get_avenrun(unsigned long *loads, unsigned long offset, int shift)
	*/		*/
	void calc_global_load(unsigned long ticks)		void calc_global_load(unsigned long ticks)
	{		{
	long active;		long active, delta;

	if (time_before(jiffies, calc_load_update + 10))		if (time_before(jiffies, calc_load_update + 10))
	return;		return;

			/*
			* Fold the 'old' idle-delta to include all NO_HZ cpus.
			*/
			delta = calc_load_fold_idle();
			if (delta)
			atomic_long_add(delta, &calc_load_tasks);

	active = atomic_long_read(&calc_load_tasks);		active = atomic_long_read(&calc_load_tasks);
	active = active > 0 ? active * FIXED_1 : 0;		active = active > 0 ? active * FIXED_1 : 0;

	@@ -2384,12 +2517,7 @@ void calc_global_load(unsigned long ticks)
	calc_load_update += LOAD_FREQ;		calc_load_update += LOAD_FREQ;

	/*		/*
	* Account one period with whatever state we found before		* In case we idled for multiple LOAD_FREQ intervals, catch up in bulk.
	* folding in the nohz state and ageing the entire idle period.
	*
	* This avoids loosing a sample when we go idle between
	* calc_load_account_active() (10 ticks ago) and now and thus
	* under-accounting.
	*/		*/
	calc_global_nohz();		calc_global_nohz();
	}		}
	@@ -2406,13 +2534,16 @@ static void calc_load_account_active(struct rq *this_rq)
	return;		return;

	delta = calc_load_fold_active(this_rq);		delta = calc_load_fold_active(this_rq);
	delta += calc_load_fold_idle();
	if (delta)		if (delta)
	atomic_long_add(delta, &calc_load_tasks);		atomic_long_add(delta, &calc_load_tasks);

	this_rq->calc_load_update += LOAD_FREQ;		this_rq->calc_load_update += LOAD_FREQ;
	}		}

			/*
			* End of global load-average stuff
			*/

	/*		/*
	* The exact cpuload at various idx values, calculated at every tick would be		* The exact cpuload at various idx values, calculated at every tick would be
	* load = (2^idx - 1) / 2^idx * load + 1 / 2^idx * cur_load		* load = (2^idx - 1) / 2^idx * load + 1 / 2^idx * cur_load

kernel/sched/idle_task.c

+0 −1

Original line number	Original line	Diff line number	Diff line
	@@ -25,7 +25,6 @@ static void check_preempt_curr_idle(struct rq rq, struct task_struct p, int fl
	static struct task_struct pick_next_task_idle(struct rq rq)		static struct task_struct pick_next_task_idle(struct rq rq)
	{		{
	schedstat_inc(rq, sched_goidle);		schedstat_inc(rq, sched_goidle);
	calc_load_account_idle(rq);
	return rq->idle;		return rq->idle;
	}		}

kernel/sched/sched.h

+0 −2

Original line number	Original line	Diff line number	Diff line
	@@ -942,8 +942,6 @@ static inline u64 sched_avg_period(void)
	return (u64)sysctl_sched_time_avg * NSEC_PER_MSEC / 2;		return (u64)sysctl_sched_time_avg * NSEC_PER_MSEC / 2;
	}		}

	void calc_load_account_idle(struct rq *this_rq);

	#ifdef CONFIG_SCHED_HRTICK		#ifdef CONFIG_SCHED_HRTICK

	/*		/*

kernel/time/tick-sched.c

+2 −0

Original line number	Original line	Diff line number	Diff line
	@@ -406,6 +406,7 @@ static void tick_nohz_stop_sched_tick(struct tick_sched *ts)
	*/		*/
	if (!ts->tick_stopped) {		if (!ts->tick_stopped) {
	select_nohz_load_balancer(1);		select_nohz_load_balancer(1);
			calc_load_enter_idle();

	ts->idle_tick = hrtimer_get_expires(&ts->sched_timer);		ts->idle_tick = hrtimer_get_expires(&ts->sched_timer);
	ts->tick_stopped = 1;		ts->tick_stopped = 1;
	@@ -597,6 +598,7 @@ void tick_nohz_idle_exit(void)
	account_idle_ticks(ticks);		account_idle_ticks(ticks);
	#endif		#endif

			calc_load_exit_idle();
	touch_softlockup_watchdog();		touch_softlockup_watchdog();
	/*		/*
	* Cancel the scheduled timer and restore the tick		* Cancel the scheduled timer and restore the tick

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