sched/cputime, s390: Implement delayed accounting of system time

The account_system_time() function is called with a cputime that
occurred while running in the kernel. The function detects which
context the CPU is currently running in and accounts the time to
the correct bucket. This forces the arch code to account the
cputime for hardirq and softirq immediately.

Such accounting function can be costly and perform unwelcome divisions
and multiplications, among others.

The arch code can delay the accounting for system time. For s390
the accounting is done once per timer tick and for each task switch.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
[ Rebase against latest linus tree and move account_system_index_scaled(). ]
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
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: Tony Luck <tony.luck@intel.com>
Cc: Wanpeng Li <wanpeng.li@hotmail.com>
Link: http://lkml.kernel.org/r/1483636310-6557-10-git-send-email-fweisbec@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 88 insertions, 48 deletions

diff --git a/arch/s390/kernel/vtime.c b/arch/s390/kernel/vtime.c
index 1b5c5ee9fc1b..1a53e0bdc90a 100644
--- a/arch/s390/kernel/vtime.c
+++ b/arch/s390/kernel/vtime.c
@@ -90,14 +90,41 @@ static void update_mt_scaling(void)
 	__this_cpu_write(mt_scaling_jiffies, jiffies_64);
 }
 
+static inline u64 update_tsk_timer(unsigned long *tsk_vtime, u64 new)
+{
+	u64 delta;
+
+	delta = new - *tsk_vtime;
+	*tsk_vtime = new;
+	return delta;
+}
+
+
+static inline u64 scale_vtime(u64 vtime)
+{
+	u64 mult = __this_cpu_read(mt_scaling_mult);
+	u64 div = __this_cpu_read(mt_scaling_div);
+
+	if (smp_cpu_mtid)
+		return vtime * mult / div;
+	return vtime;
+}
+
+static void account_system_index_scaled(struct task_struct *p,
+					cputime_t cputime, cputime_t scaled,
+					enum cpu_usage_stat index)
+{
+	p->stimescaled += scaled;
+	account_system_index_time(p, cputime, index);
+}
+
 /*
  * Update process times based on virtual cpu times stored by entry.S
  * to the lowcore fields user_timer, system_timer & steal_clock.
  */
 static int do_account_vtime(struct task_struct *tsk)
 {
-	u64 timer, clock, user, system, steal;
-	u64 user_scaled, system_scaled;
+	u64 timer, clock, user, guest, system, hardirq, softirq, steal;
 
 	timer = S390_lowcore.last_update_timer;
 	clock = S390_lowcore.last_update_clock;
@@ -110,36 +137,53 @@ static int do_account_vtime(struct task_struct *tsk)
 #endif
 		: "=m" (S390_lowcore.last_update_timer),
 		  "=m" (S390_lowcore.last_update_clock));
-	S390_lowcore.system_timer += timer - S390_lowcore.last_update_timer;
-	S390_lowcore.steal_timer += S390_lowcore.last_update_clock - clock;
+	clock = S390_lowcore.last_update_clock - clock;
+	timer -= S390_lowcore.last_update_timer;
+
+	if (hardirq_count())
+		S390_lowcore.hardirq_timer += timer;
+	else
+		S390_lowcore.system_timer += timer;
 
 	/* Update MT utilization calculation */
 	if (smp_cpu_mtid &&
 	    time_after64(jiffies_64, this_cpu_read(mt_scaling_jiffies)))
 		update_mt_scaling();
 
-	user = S390_lowcore.user_timer - tsk->thread.user_timer;
-	S390_lowcore.steal_timer -= user;
-	tsk->thread.user_timer = S390_lowcore.user_timer;
-
-	system = S390_lowcore.system_timer - tsk->thread.system_timer;
-	S390_lowcore.steal_timer -= system;
-	tsk->thread.system_timer = S390_lowcore.system_timer;
-
-	user_scaled = user;
-	system_scaled = system;
-	/* Do MT utilization scaling */
-	if (smp_cpu_mtid) {
-		u64 mult = __this_cpu_read(mt_scaling_mult);
-		u64 div = __this_cpu_read(mt_scaling_div);
+	/* Calculate cputime delta */
+	user = update_tsk_timer(&tsk->thread.user_timer,
+				READ_ONCE(S390_lowcore.user_timer));
+	guest = update_tsk_timer(&tsk->thread.guest_timer,
+				 READ_ONCE(S390_lowcore.guest_timer));
+	system = update_tsk_timer(&tsk->thread.system_timer,
+				  READ_ONCE(S390_lowcore.system_timer));
+	hardirq = update_tsk_timer(&tsk->thread.hardirq_timer,
+				   READ_ONCE(S390_lowcore.hardirq_timer));
+	softirq = update_tsk_timer(&tsk->thread.softirq_timer,
+				   READ_ONCE(S390_lowcore.softirq_timer));
+	S390_lowcore.steal_timer +=
+		clock - user - guest - system - hardirq - softirq;
+
+	/* Push account value */
+	if (user) {
+		account_user_time(tsk, user);
+		tsk->utimescaled += scale_vtime(user);
+	}
 
-		user_scaled = (user_scaled * mult) / div;
-		system_scaled = (system_scaled * mult) / div;
+	if (guest) {
+		account_guest_time(tsk, guest);
+		tsk->utimescaled += scale_vtime(guest);
 	}
-	account_user_time(tsk, user);
-	tsk->utimescaled += user_scaled;
-	account_system_time(tsk, 0, system);
-	tsk->stimescaled += system_scaled;
+
+	if (system)
+		account_system_index_scaled(tsk, system, scale_vtime(system),
+					    CPUTIME_SYSTEM);
+	if (hardirq)
+		account_system_index_scaled(tsk, hardirq, scale_vtime(hardirq),
+					    CPUTIME_IRQ);
+	if (softirq)
+		account_system_index_scaled(tsk, softirq, scale_vtime(softirq),
+					    CPUTIME_SOFTIRQ);
 
 	steal = S390_lowcore.steal_timer;
 	if ((s64) steal > 0) {
@@ -147,16 +191,22 @@ static int do_account_vtime(struct task_struct *tsk)
 		account_steal_time(steal);
 	}
 
-	return virt_timer_forward(user + system);
+	return virt_timer_forward(user + guest + system + hardirq + softirq);
 }
 
 void vtime_task_switch(struct task_struct *prev)
 {
 	do_account_vtime(prev);
 	prev->thread.user_timer = S390_lowcore.user_timer;
+	prev->thread.guest_timer = S390_lowcore.guest_timer;
 	prev->thread.system_timer = S390_lowcore.system_timer;
+	prev->thread.hardirq_timer = S390_lowcore.hardirq_timer;
+	prev->thread.softirq_timer = S390_lowcore.softirq_timer;
 	S390_lowcore.user_timer = current->thread.user_timer;
+	S390_lowcore.guest_timer = current->thread.guest_timer;
 	S390_lowcore.system_timer = current->thread.system_timer;
+	S390_lowcore.hardirq_timer = current->thread.hardirq_timer;
+	S390_lowcore.softirq_timer = current->thread.softirq_timer;
 }
 
 /*
@@ -176,32 +226,22 @@ void vtime_account_user(struct task_struct *tsk)
  */
 void vtime_account_irq_enter(struct task_struct *tsk)
 {
-	u64 timer, system, system_scaled;
+	u64 timer;
 
 	timer = S390_lowcore.last_update_timer;
 	S390_lowcore.last_update_timer = get_vtimer();
-	S390_lowcore.system_timer += timer - S390_lowcore.last_update_timer;
-
-	/* Update MT utilization calculation */
-	if (smp_cpu_mtid &&
-	    time_after64(jiffies_64, this_cpu_read(mt_scaling_jiffies)))
-		update_mt_scaling();
-
-	system = S390_lowcore.system_timer - tsk->thread.system_timer;
-	S390_lowcore.steal_timer -= system;
-	tsk->thread.system_timer = S390_lowcore.system_timer;
-	system_scaled = system;
-	/* Do MT utilization scaling */
-	if (smp_cpu_mtid) {
-		u64 mult = __this_cpu_read(mt_scaling_mult);
-		u64 div = __this_cpu_read(mt_scaling_div);
-
-		system_scaled = (system_scaled * mult) / div;
-	}
-	account_system_time(tsk, 0, system);
-	tsk->stimescaled += system_scaled;
-
-	virt_timer_forward(system);
+	timer -= S390_lowcore.last_update_timer;
+
+	if ((tsk->flags & PF_VCPU) && (irq_count() == 0))
+		S390_lowcore.guest_timer += timer;
+	else if (hardirq_count())
+		S390_lowcore.hardirq_timer += timer;
+	else if (in_serving_softirq())
+		S390_lowcore.softirq_timer += timer;
+	else
+		S390_lowcore.system_timer += timer;
+
+	virt_timer_forward(timer);
 }
 EXPORT_SYMBOL_GPL(vtime_account_irq_enter);