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Message-ID: <171981760706.2215.13966714897751148165.tip-bot2@tip-bot2>
Date: Mon, 01 Jul 2024 07:06:47 -0000
From: "tip-bot2 for John Stultz" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Jimmy Shiu <jimmyshiu@...gle.com>, Peter Zijlstra <peterz@...radead.org>,
John Stultz <jstultz@...gle.com>, Chengming Zhou <chengming.zhou@...ux.dev>,
Qais Yousef <qyousef@...alina.io>, x86@...nel.org,
linux-kernel@...r.kernel.org
Subject: [tip: sched/urgent] sched: Move psi_account_irqtime() out of
update_rq_clock_task() hotpath
The following commit has been merged into the sched/urgent branch of tip:
Commit-ID: 45655e7bd66c78920b0a579d146aa67788545e3c
Gitweb: https://git.kernel.org/tip/45655e7bd66c78920b0a579d146aa67788545e3c
Author: John Stultz <jstultz@...gle.com>
AuthorDate: Tue, 18 Jun 2024 14:58:55 -07:00
Committer: Peter Zijlstra <peterz@...radead.org>
CommitterDate: Tue, 25 Jun 2024 10:43:42 +02:00
sched: Move psi_account_irqtime() out of update_rq_clock_task() hotpath
It was reported that in moving to 6.1, a larger then 10%
regression was seen in the performance of
clock_gettime(CLOCK_THREAD_CPUTIME_ID,...).
Using a simple reproducer, I found:
5.10:
100000000 calls in 24345994193 ns => 243.460 ns per call
100000000 calls in 24288172050 ns => 242.882 ns per call
100000000 calls in 24289135225 ns => 242.891 ns per call
6.1:
100000000 calls in 28248646742 ns => 282.486 ns per call
100000000 calls in 28227055067 ns => 282.271 ns per call
100000000 calls in 28177471287 ns => 281.775 ns per call
The cause of this was finally narrowed down to the addition of
psi_account_irqtime() in update_rq_clock_task(), in commit
52b1364ba0b1 ("sched/psi: Add PSI_IRQ to track IRQ/SOFTIRQ
pressure").
In my initial attempt to resolve this, I leaned towards moving
all accounting work out of the clock_gettime() call path, but it
wasn't very pretty, so it will have to wait for a later deeper
rework. Instead, Peter shared this approach:
Rework psi_account_irqtime() to use its own psi_irq_time base
for accounting, and move it out of the hotpath, calling it
instead from sched_tick() and __schedule().
In testing this, we found the importance of ensuring
psi_account_irqtime() is run under the rq_lock, which Johannes
Weiner helpfully explained, so also add some lockdep annotations
to make that requirement clear.
With this change the performance is back in-line with 5.10:
6.1+fix:
100000000 calls in 24297324597 ns => 242.973 ns per call
100000000 calls in 24318869234 ns => 243.189 ns per call
100000000 calls in 24291564588 ns => 242.916 ns per call
Reported-by: Jimmy Shiu <jimmyshiu@...gle.com>
Originally-by: Peter Zijlstra <peterz@...radead.org>
Signed-off-by: John Stultz <jstultz@...gle.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: Chengming Zhou <chengming.zhou@...ux.dev>
Reviewed-by: Qais Yousef <qyousef@...alina.io>
Link: https://lore.kernel.org/r/20240618215909.4099720-1-jstultz@google.com
---
kernel/sched/core.c | 7 +++++--
kernel/sched/psi.c | 21 ++++++++++++++++-----
kernel/sched/sched.h | 1 +
kernel/sched/stats.h | 11 ++++++++---
4 files changed, 30 insertions(+), 10 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index bcf2c4c..59ce084 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -723,7 +723,6 @@ static void update_rq_clock_task(struct rq *rq, s64 delta)
rq->prev_irq_time += irq_delta;
delta -= irq_delta;
- psi_account_irqtime(rq->curr, irq_delta);
delayacct_irq(rq->curr, irq_delta);
#endif
#ifdef CONFIG_PARAVIRT_TIME_ACCOUNTING
@@ -5665,7 +5664,7 @@ void sched_tick(void)
{
int cpu = smp_processor_id();
struct rq *rq = cpu_rq(cpu);
- struct task_struct *curr = rq->curr;
+ struct task_struct *curr;
struct rq_flags rf;
unsigned long hw_pressure;
u64 resched_latency;
@@ -5677,6 +5676,9 @@ void sched_tick(void)
rq_lock(rq, &rf);
+ curr = rq->curr;
+ psi_account_irqtime(rq, curr, NULL);
+
update_rq_clock(rq);
hw_pressure = arch_scale_hw_pressure(cpu_of(rq));
update_hw_load_avg(rq_clock_task(rq), rq, hw_pressure);
@@ -6737,6 +6739,7 @@ static void __sched notrace __schedule(unsigned int sched_mode)
++*switch_count;
migrate_disable_switch(rq, prev);
+ psi_account_irqtime(rq, prev, next);
psi_sched_switch(prev, next, !task_on_rq_queued(prev));
trace_sched_switch(sched_mode & SM_MASK_PREEMPT, prev, next, prev_state);
diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
index 7b4aa58..507d7b8 100644
--- a/kernel/sched/psi.c
+++ b/kernel/sched/psi.c
@@ -773,6 +773,7 @@ static void psi_group_change(struct psi_group *group, int cpu,
enum psi_states s;
u32 state_mask;
+ lockdep_assert_rq_held(cpu_rq(cpu));
groupc = per_cpu_ptr(group->pcpu, cpu);
/*
@@ -991,22 +992,32 @@ void psi_task_switch(struct task_struct *prev, struct task_struct *next,
}
#ifdef CONFIG_IRQ_TIME_ACCOUNTING
-void psi_account_irqtime(struct task_struct *task, u32 delta)
+void psi_account_irqtime(struct rq *rq, struct task_struct *curr, struct task_struct *prev)
{
- int cpu = task_cpu(task);
+ int cpu = task_cpu(curr);
struct psi_group *group;
struct psi_group_cpu *groupc;
- u64 now;
+ u64 now, irq;
+ s64 delta;
if (static_branch_likely(&psi_disabled))
return;
- if (!task->pid)
+ if (!curr->pid)
+ return;
+
+ lockdep_assert_rq_held(rq);
+ group = task_psi_group(curr);
+ if (prev && task_psi_group(prev) == group)
return;
now = cpu_clock(cpu);
+ irq = irq_time_read(cpu);
+ delta = (s64)(irq - rq->psi_irq_time);
+ if (delta < 0)
+ return;
+ rq->psi_irq_time = irq;
- group = task_psi_group(task);
do {
if (!group->enabled)
continue;
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index a831af1..ef20c61 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1126,6 +1126,7 @@ struct rq {
#ifdef CONFIG_IRQ_TIME_ACCOUNTING
u64 prev_irq_time;
+ u64 psi_irq_time;
#endif
#ifdef CONFIG_PARAVIRT
u64 prev_steal_time;
diff --git a/kernel/sched/stats.h b/kernel/sched/stats.h
index 38f3698..b02dfc3 100644
--- a/kernel/sched/stats.h
+++ b/kernel/sched/stats.h
@@ -110,8 +110,12 @@ __schedstats_from_se(struct sched_entity *se)
void psi_task_change(struct task_struct *task, int clear, int set);
void psi_task_switch(struct task_struct *prev, struct task_struct *next,
bool sleep);
-void psi_account_irqtime(struct task_struct *task, u32 delta);
-
+#ifdef CONFIG_IRQ_TIME_ACCOUNTING
+void psi_account_irqtime(struct rq *rq, struct task_struct *curr, struct task_struct *prev);
+#else
+static inline void psi_account_irqtime(struct rq *rq, struct task_struct *curr,
+ struct task_struct *prev) {}
+#endif /*CONFIG_IRQ_TIME_ACCOUNTING */
/*
* PSI tracks state that persists across sleeps, such as iowaits and
* memory stalls. As a result, it has to distinguish between sleeps,
@@ -192,7 +196,8 @@ static inline void psi_ttwu_dequeue(struct task_struct *p) {}
static inline void psi_sched_switch(struct task_struct *prev,
struct task_struct *next,
bool sleep) {}
-static inline void psi_account_irqtime(struct task_struct *task, u32 delta) {}
+static inline void psi_account_irqtime(struct rq *rq, struct task_struct *curr,
+ struct task_struct *prev) {}
#endif /* CONFIG_PSI */
#ifdef CONFIG_SCHED_INFO
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