[PATCH 4.9 28/35] sched/cputime: Increment kcpustat directly on irqtime account

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Frederic Weisbecker <fweisbec@gmail.com>

commit a499a5a14dbd1d0315a96fc62a8798059325e9e6 upstream.

The irqtime is accounted is nsecs and stored in
cpu_irq_time.hardirq_time and cpu_irq_time.softirq_time. Once the
accumulated amount reaches a new jiffy, this one gets accounted to the
kcpustat.

This was necessary when kcpustat was stored in cputime_t, which could at
worst have jiffies granularity. But now kcpustat is stored in nsecs
so this whole discretization game with temporary irqtime storage has
become unnecessary.

We can now directly account the irqtime to the kcpustat.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Stanislaw Gruszka <sgruszka@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Wanpeng Li <wanpeng.li@hotmail.com>
Link: http://lkml.kernel.org/r/1485832191-26889-17-git-send-email-fweisbec@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Ivan Delalande <colona@arista.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 kernel/sched/cputime.c |   50 ++++++++++++++++---------------------------------
 kernel/sched/sched.h   |    7 +++---
 2 files changed, 21 insertions(+), 36 deletions(-)

--- a/kernel/sched/cputime.c
+++ b/kernel/sched/cputime.c
@@ -44,6 +44,7 @@ void disable_sched_clock_irqtime(void)
 void irqtime_account_irq(struct task_struct *curr)
 {
 	struct irqtime *irqtime = this_cpu_ptr(&cpu_irqtime);
+	u64 *cpustat = kcpustat_this_cpu->cpustat;
 	s64 delta;
 	int cpu;
 
@@ -61,49 +62,35 @@ void irqtime_account_irq(struct task_str
 	 * in that case, so as not to confuse scheduler with a special task
 	 * that do not consume any time, but still wants to run.
 	 */
-	if (hardirq_count())
-		irqtime->hardirq_time += delta;
-	else if (in_serving_softirq() && curr != this_cpu_ksoftirqd())
-		irqtime->softirq_time += delta;
+	if (hardirq_count()) {
+		cpustat[CPUTIME_IRQ] += delta;
+		irqtime->tick_delta += delta;
+	} else if (in_serving_softirq() && curr != this_cpu_ksoftirqd()) {
+		cpustat[CPUTIME_SOFTIRQ] += delta;
+		irqtime->tick_delta += delta;
+	}
 
 	u64_stats_update_end(&irqtime->sync);
 }
 EXPORT_SYMBOL_GPL(irqtime_account_irq);
 
-static cputime_t irqtime_account_update(u64 irqtime, int idx, cputime_t maxtime)
+static cputime_t irqtime_tick_accounted(cputime_t maxtime)
 {
-	u64 *cpustat = kcpustat_this_cpu->cpustat;
-	cputime_t irq_cputime;
-
-	irq_cputime = nsecs_to_cputime64(irqtime - cpustat[idx]);
-	irq_cputime = min(irq_cputime, maxtime);
-	cpustat[idx] += cputime_to_nsecs(irq_cputime);
-
-	return irq_cputime;
-}
+	struct irqtime *irqtime = this_cpu_ptr(&cpu_irqtime);
+	cputime_t delta;
 
-static cputime_t irqtime_account_hi_update(cputime_t maxtime)
-{
-	return irqtime_account_update(__this_cpu_read(cpu_irqtime.hardirq_time),
-				      CPUTIME_IRQ, maxtime);
-}
+	delta = nsecs_to_cputime(irqtime->tick_delta);
+	delta = min(delta, maxtime);
+	irqtime->tick_delta -= cputime_to_nsecs(delta);
 
-static cputime_t irqtime_account_si_update(cputime_t maxtime)
-{
-	return irqtime_account_update(__this_cpu_read(cpu_irqtime.softirq_time),
-				      CPUTIME_SOFTIRQ, maxtime);
+	return delta;
 }
 
 #else /* CONFIG_IRQ_TIME_ACCOUNTING */
 
 #define sched_clock_irqtime	(0)
 
-static cputime_t irqtime_account_hi_update(cputime_t dummy)
-{
-	return 0;
-}
-
-static cputime_t irqtime_account_si_update(cputime_t dummy)
+static cputime_t irqtime_tick_accounted(cputime_t dummy)
 {
 	return 0;
 }
@@ -290,10 +277,7 @@ static inline cputime_t account_other_ti
 	accounted = steal_account_process_time(max);
 
 	if (accounted < max)
-		accounted += irqtime_account_hi_update(max - accounted);
-
-	if (accounted < max)
-		accounted += irqtime_account_si_update(max - accounted);
+		accounted += irqtime_tick_accounted(max - accounted);
 
 	return accounted;
 }
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -4,6 +4,7 @@
 #include <linux/sched/rt.h>
 #include <linux/u64_stats_sync.h>
 #include <linux/sched/deadline.h>
+#include <linux/kernel_stat.h>
 #include <linux/binfmts.h>
 #include <linux/mutex.h>
 #include <linux/spinlock.h>
@@ -1742,8 +1743,7 @@ static inline void nohz_balance_exit_idl
 
 #ifdef CONFIG_IRQ_TIME_ACCOUNTING
 struct irqtime {
-	u64			hardirq_time;
-	u64			softirq_time;
+	u64			tick_delta;
 	u64			irq_start_time;
 	struct u64_stats_sync	sync;
 };
@@ -1753,12 +1753,13 @@ DECLARE_PER_CPU(struct irqtime, cpu_irqt
 static inline u64 irq_time_read(int cpu)
 {
 	struct irqtime *irqtime = &per_cpu(cpu_irqtime, cpu);
+	u64 *cpustat = kcpustat_cpu(cpu).cpustat;
 	unsigned int seq;
 	u64 total;
 
 	do {
 		seq = __u64_stats_fetch_begin(&irqtime->sync);
-		total = irqtime->softirq_time + irqtime->hardirq_time;
+		total = cpustat[CPUTIME_SOFTIRQ] + cpustat[CPUTIME_IRQ];
 	} while (__u64_stats_fetch_retry(&irqtime->sync, seq));
 
 	return total;