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![Johannes Weiner](/assets/img/avatar_default.png)
Mel Gorman reports a hackbench regression with psi that would prohibit shipping the suse kernel with it default-enabled, but he'd still like users to be able to opt in at little to no cost to others. With the current combination of CONFIG_PSI and the psi_disabled bool set from the commandline, this is a challenge. Do the following things to make it easier: 1. Add a config option CONFIG_PSI_DEFAULT_DISABLED that allows distros to enable CONFIG_PSI in their kernel but leave the feature disabled unless a user requests it at boot-time. To avoid double negatives, rename psi_disabled= to psi=. 2. Make psi_disabled a static branch to eliminate any branch costs when the feature is disabled. In terms of numbers before and after this patch, Mel says: : The following is a comparision using CONFIG_PSI=n as a baseline against : your patch and a vanilla kernel : : 4.20.0-rc4 4.20.0-rc4 4.20.0-rc4 : kconfigdisable-v1r1 vanilla psidisable-v1r1 : Amean 1 1.3100 ( 0.00%) 1.3923 ( -6.28%) 1.3427 ( -2.49%) : Amean 3 3.8860 ( 0.00%) 4.1230 * -6.10%* 3.8860 ( -0.00%) : Amean 5 6.8847 ( 0.00%) 8.0390 * -16.77%* 6.7727 ( 1.63%) : Amean 7 9.9310 ( 0.00%) 10.8367 * -9.12%* 9.9910 ( -0.60%) : Amean 12 16.6577 ( 0.00%) 18.2363 * -9.48%* 17.1083 ( -2.71%) : Amean 18 26.5133 ( 0.00%) 27.8833 * -5.17%* 25.7663 ( 2.82%) : Amean 24 34.3003 ( 0.00%) 34.6830 ( -1.12%) 32.0450 ( 6.58%) : Amean 30 40.0063 ( 0.00%) 40.5800 ( -1.43%) 41.5087 ( -3.76%) : Amean 32 40.1407 ( 0.00%) 41.2273 ( -2.71%) 39.9417 ( 0.50%) : : It's showing that the vanilla kernel takes a hit (as the bisection : indicated it would) and that disabling PSI by default is reasonably : close in terms of performance for this particular workload on this : particular machine so; Link: http://lkml.kernel.org/r/20181127165329.GA29728@cmpxchg.org Signed-off-by: Johannes Weiner <hannes@cmpxchg.org> Tested-by: Mel Gorman <mgorman@techsingularity.net> Reported-by: Mel Gorman <mgorman@techsingularity.net> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
253 lines
7.5 KiB
C
253 lines
7.5 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifdef CONFIG_SCHEDSTATS
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/*
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* Expects runqueue lock to be held for atomicity of update
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*/
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static inline void
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rq_sched_info_arrive(struct rq *rq, unsigned long long delta)
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{
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if (rq) {
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rq->rq_sched_info.run_delay += delta;
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rq->rq_sched_info.pcount++;
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}
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}
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/*
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* Expects runqueue lock to be held for atomicity of update
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*/
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static inline void
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rq_sched_info_depart(struct rq *rq, unsigned long long delta)
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{
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if (rq)
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rq->rq_cpu_time += delta;
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}
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static inline void
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rq_sched_info_dequeued(struct rq *rq, unsigned long long delta)
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{
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if (rq)
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rq->rq_sched_info.run_delay += delta;
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}
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#define schedstat_enabled() static_branch_unlikely(&sched_schedstats)
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#define __schedstat_inc(var) do { var++; } while (0)
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#define schedstat_inc(var) do { if (schedstat_enabled()) { var++; } } while (0)
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#define __schedstat_add(var, amt) do { var += (amt); } while (0)
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#define schedstat_add(var, amt) do { if (schedstat_enabled()) { var += (amt); } } while (0)
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#define __schedstat_set(var, val) do { var = (val); } while (0)
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#define schedstat_set(var, val) do { if (schedstat_enabled()) { var = (val); } } while (0)
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#define schedstat_val(var) (var)
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#define schedstat_val_or_zero(var) ((schedstat_enabled()) ? (var) : 0)
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#else /* !CONFIG_SCHEDSTATS: */
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static inline void rq_sched_info_arrive (struct rq *rq, unsigned long long delta) { }
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static inline void rq_sched_info_dequeued(struct rq *rq, unsigned long long delta) { }
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static inline void rq_sched_info_depart (struct rq *rq, unsigned long long delta) { }
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# define schedstat_enabled() 0
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# define __schedstat_inc(var) do { } while (0)
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# define schedstat_inc(var) do { } while (0)
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# define __schedstat_add(var, amt) do { } while (0)
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# define schedstat_add(var, amt) do { } while (0)
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# define __schedstat_set(var, val) do { } while (0)
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# define schedstat_set(var, val) do { } while (0)
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# define schedstat_val(var) 0
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# define schedstat_val_or_zero(var) 0
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#endif /* CONFIG_SCHEDSTATS */
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#ifdef CONFIG_PSI
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/*
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* PSI tracks state that persists across sleeps, such as iowaits and
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* memory stalls. As a result, it has to distinguish between sleeps,
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* where a task's runnable state changes, and requeues, where a task
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* and its state are being moved between CPUs and runqueues.
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*/
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static inline void psi_enqueue(struct task_struct *p, bool wakeup)
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{
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int clear = 0, set = TSK_RUNNING;
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if (static_branch_likely(&psi_disabled))
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return;
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if (!wakeup || p->sched_psi_wake_requeue) {
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if (p->flags & PF_MEMSTALL)
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set |= TSK_MEMSTALL;
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if (p->sched_psi_wake_requeue)
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p->sched_psi_wake_requeue = 0;
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} else {
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if (p->in_iowait)
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clear |= TSK_IOWAIT;
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}
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psi_task_change(p, clear, set);
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}
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static inline void psi_dequeue(struct task_struct *p, bool sleep)
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{
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int clear = TSK_RUNNING, set = 0;
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if (static_branch_likely(&psi_disabled))
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return;
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if (!sleep) {
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if (p->flags & PF_MEMSTALL)
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clear |= TSK_MEMSTALL;
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} else {
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if (p->in_iowait)
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set |= TSK_IOWAIT;
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}
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psi_task_change(p, clear, set);
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}
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static inline void psi_ttwu_dequeue(struct task_struct *p)
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{
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if (static_branch_likely(&psi_disabled))
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return;
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/*
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* Is the task being migrated during a wakeup? Make sure to
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* deregister its sleep-persistent psi states from the old
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* queue, and let psi_enqueue() know it has to requeue.
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*/
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if (unlikely(p->in_iowait || (p->flags & PF_MEMSTALL))) {
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struct rq_flags rf;
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struct rq *rq;
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int clear = 0;
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if (p->in_iowait)
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clear |= TSK_IOWAIT;
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if (p->flags & PF_MEMSTALL)
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clear |= TSK_MEMSTALL;
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rq = __task_rq_lock(p, &rf);
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psi_task_change(p, clear, 0);
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p->sched_psi_wake_requeue = 1;
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__task_rq_unlock(rq, &rf);
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}
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}
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static inline void psi_task_tick(struct rq *rq)
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{
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if (static_branch_likely(&psi_disabled))
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return;
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if (unlikely(rq->curr->flags & PF_MEMSTALL))
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psi_memstall_tick(rq->curr, cpu_of(rq));
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}
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#else /* CONFIG_PSI */
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static inline void psi_enqueue(struct task_struct *p, bool wakeup) {}
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static inline void psi_dequeue(struct task_struct *p, bool sleep) {}
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static inline void psi_ttwu_dequeue(struct task_struct *p) {}
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static inline void psi_task_tick(struct rq *rq) {}
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#endif /* CONFIG_PSI */
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#ifdef CONFIG_SCHED_INFO
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static inline void sched_info_reset_dequeued(struct task_struct *t)
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{
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t->sched_info.last_queued = 0;
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}
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/*
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* We are interested in knowing how long it was from the *first* time a
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* task was queued to the time that it finally hit a CPU, we call this routine
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* from dequeue_task() to account for possible rq->clock skew across CPUs. The
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* delta taken on each CPU would annul the skew.
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*/
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static inline void sched_info_dequeued(struct rq *rq, struct task_struct *t)
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{
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unsigned long long now = rq_clock(rq), delta = 0;
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if (unlikely(sched_info_on()))
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if (t->sched_info.last_queued)
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delta = now - t->sched_info.last_queued;
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sched_info_reset_dequeued(t);
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t->sched_info.run_delay += delta;
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rq_sched_info_dequeued(rq, delta);
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}
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/*
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* Called when a task finally hits the CPU. We can now calculate how
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* long it was waiting to run. We also note when it began so that we
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* can keep stats on how long its timeslice is.
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*/
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static void sched_info_arrive(struct rq *rq, struct task_struct *t)
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{
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unsigned long long now = rq_clock(rq), delta = 0;
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if (t->sched_info.last_queued)
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delta = now - t->sched_info.last_queued;
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sched_info_reset_dequeued(t);
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t->sched_info.run_delay += delta;
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t->sched_info.last_arrival = now;
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t->sched_info.pcount++;
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rq_sched_info_arrive(rq, delta);
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}
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/*
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* This function is only called from enqueue_task(), but also only updates
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* the timestamp if it is already not set. It's assumed that
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* sched_info_dequeued() will clear that stamp when appropriate.
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*/
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static inline void sched_info_queued(struct rq *rq, struct task_struct *t)
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{
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if (unlikely(sched_info_on())) {
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if (!t->sched_info.last_queued)
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t->sched_info.last_queued = rq_clock(rq);
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}
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}
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/*
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* Called when a process ceases being the active-running process involuntarily
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* due, typically, to expiring its time slice (this may also be called when
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* switching to the idle task). Now we can calculate how long we ran.
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* Also, if the process is still in the TASK_RUNNING state, call
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* sched_info_queued() to mark that it has now again started waiting on
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* the runqueue.
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*/
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static inline void sched_info_depart(struct rq *rq, struct task_struct *t)
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{
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unsigned long long delta = rq_clock(rq) - t->sched_info.last_arrival;
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rq_sched_info_depart(rq, delta);
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if (t->state == TASK_RUNNING)
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sched_info_queued(rq, t);
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}
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/*
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* Called when tasks are switched involuntarily due, typically, to expiring
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* their time slice. (This may also be called when switching to or from
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* the idle task.) We are only called when prev != next.
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*/
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static inline void
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__sched_info_switch(struct rq *rq, struct task_struct *prev, struct task_struct *next)
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{
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/*
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* prev now departs the CPU. It's not interesting to record
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* stats about how efficient we were at scheduling the idle
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* process, however.
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*/
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if (prev != rq->idle)
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sched_info_depart(rq, prev);
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if (next != rq->idle)
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sched_info_arrive(rq, next);
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}
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static inline void
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sched_info_switch(struct rq *rq, struct task_struct *prev, struct task_struct *next)
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{
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if (unlikely(sched_info_on()))
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__sched_info_switch(rq, prev, next);
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}
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#else /* !CONFIG_SCHED_INFO: */
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# define sched_info_queued(rq, t) do { } while (0)
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# define sched_info_reset_dequeued(t) do { } while (0)
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# define sched_info_dequeued(rq, t) do { } while (0)
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# define sched_info_depart(rq, t) do { } while (0)
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# define sched_info_arrive(rq, next) do { } while (0)
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# define sched_info_switch(rq, t, next) do { } while (0)
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#endif /* CONFIG_SCHED_INFO */
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