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From a4b2fa58f0b8dabae3f30be80fe317da32c5b121 Mon Sep 17 00:00:00 2001
From: Thomas Gleixner <tglx@linutronix.de>
Date: Tue, 9 Mar 2021 09:55:54 +0100
Subject: [PATCH 147/323] irqtime: Make accounting correct on RT
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/5.10/older/patches-5.10.204-rt100.tar.xz
vtime_account_irq and irqtime_account_irq() base checks on preempt_count()
which fails on RT because preempt_count() does not contain the softirq
accounting which is seperate on RT.
These checks do not need the full preempt count as they only operate on the
hard and softirq sections.
Use irq_count() instead which provides the correct value on both RT and non
RT kernels. The compiler is clever enough to fold the masking for !RT:
99b: 65 8b 05 00 00 00 00 mov %gs:0x0(%rip),%eax
- 9a2: 25 ff ff ff 7f and $0x7fffffff,%eax
+ 9a2: 25 00 ff ff 00 and $0xffff00,%eax
Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
kernel/sched/cputime.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
index 02a7932c7383..02a5aa60fe7e 100644
--- a/kernel/sched/cputime.c
+++ b/kernel/sched/cputime.c
@@ -60,7 +60,7 @@ void irqtime_account_irq(struct task_struct *curr, unsigned int offset)
cpu = smp_processor_id();
delta = sched_clock_cpu(cpu) - irqtime->irq_start_time;
irqtime->irq_start_time += delta;
- pc = preempt_count() - offset;
+ pc = irq_count() - offset;
/*
* We do not account for softirq time from ksoftirqd here.
@@ -421,7 +421,7 @@ void vtime_task_switch(struct task_struct *prev)
void vtime_account_irq(struct task_struct *tsk, unsigned int offset)
{
- unsigned int pc = preempt_count() - offset;
+ unsigned int pc = irq_count() - offset;
if (pc & HARDIRQ_OFFSET) {
vtime_account_hardirq(tsk);
--
2.43.0
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