s390/vtime: correct scaled cputime of partially idle CPUs

The calculation for the SMT scaling factor for a hardware thread
which has been partially idle needs to disregard the cycles spent
by the other threads of the core while the thread is idle.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 37 insertions, 29 deletions

diff --git a/arch/s390/kernel/vtime.c b/arch/s390/kernel/vtime.c
index c8653435c70d..dafc44f519c3 100644
--- a/arch/s390/kernel/vtime.c
+++ b/arch/s390/kernel/vtime.c
@@ -25,7 +25,7 @@ static DEFINE_SPINLOCK(virt_timer_lock);
 static atomic64_t virt_timer_current;
 static atomic64_t virt_timer_elapsed;
 
-static DEFINE_PER_CPU(u64, mt_cycles[32]);
+DEFINE_PER_CPU(u64, mt_cycles[8]);
 static DEFINE_PER_CPU(u64, mt_scaling_mult) = { 1 };
 static DEFINE_PER_CPU(u64, mt_scaling_div) = { 1 };
 static DEFINE_PER_CPU(u64, mt_scaling_jiffies);
@@ -60,6 +60,34 @@ static inline int virt_timer_forward(u64 elapsed)
         return elapsed >= atomic64_read(&virt_timer_current);
 }
 
+static void update_mt_scaling(void)
+{
+        u64 cycles_new[8], *cycles_old;
+        u64 delta, fac, mult, div;
+        int i;
+
+        stcctm5(smp_cpu_mtid + 1, cycles_new);
+        cycles_old = this_cpu_ptr(mt_cycles);
+        fac = 1;
+        mult = div = 0;
+        for (i = 0; i <= smp_cpu_mtid; i++) {
+                delta = cycles_new[i] - cycles_old[i];
+                div += delta;
+                mult *= i + 1;
+                mult += delta * fac;
+                fac *= i + 1;
+        }
+        div *= fac;
+        if (div > 0) {
+                /* Update scaling factor */
+                __this_cpu_write(mt_scaling_mult, mult);
+                __this_cpu_write(mt_scaling_div, div);
+                memcpy(cycles_old, cycles_new,
+                       sizeof(u64) * (smp_cpu_mtid + 1));
+        }
+        __this_cpu_write(mt_scaling_jiffies, jiffies_64);
+}
+
 /*
  * Update process times based on virtual cpu times stored by entry.S
  * to the lowcore fields user_timer, system_timer & steal_clock.
@@ -69,7 +97,6 @@ static int do_account_vtime(struct task_struct *tsk, int hardirq_offset)
         struct thread_info *ti = task_thread_info(tsk);
         u64 timer, clock, user, system, steal;
         u64 user_scaled, system_scaled;
-        int i;
 
         timer = S390_lowcore.last_update_timer;
         clock = S390_lowcore.last_update_clock;
@@ -85,34 +112,10 @@ static int do_account_vtime(struct task_struct *tsk, int hardirq_offset)
         S390_lowcore.system_timer += timer - S390_lowcore.last_update_timer;
         S390_lowcore.steal_timer += S390_lowcore.last_update_clock - clock;
 
-        /* Do MT utilization calculation */
+        /* Update MT utilization calculation */
         if (smp_cpu_mtid &&
-            time_after64(jiffies_64, __this_cpu_read(mt_scaling_jiffies))) {
-                u64 cycles_new[32], *cycles_old;
-                u64 delta, fac, mult, div;
-
-                cycles_old = this_cpu_ptr(mt_cycles);
-                if (stcctm5(smp_cpu_mtid + 1, cycles_new) < 2) {
-                        fac = 1;
-                        mult = div = 0;
-                        for (i = 0; i <= smp_cpu_mtid; i++) {
-                                delta = cycles_new[i] - cycles_old[i];
-                                div += delta;
-                                mult *= i + 1;
-                                mult += delta * fac;
-                                fac *= i + 1;
-                        }
-                        div *= fac;
-                        if (div > 0) {
-                                /* Update scaling factor */
-                                __this_cpu_write(mt_scaling_mult, mult);
-                                __this_cpu_write(mt_scaling_div, div);
-                                memcpy(cycles_old, cycles_new,
-                                       sizeof(u64) * (smp_cpu_mtid + 1));
-                        }
-                }
-                __this_cpu_write(mt_scaling_jiffies, jiffies_64);
-        }
+            time_after64(jiffies_64, this_cpu_read(mt_scaling_jiffies)))
+                update_mt_scaling();
 
         user = S390_lowcore.user_timer - ti->user_timer;
         S390_lowcore.steal_timer -= user;
@@ -181,6 +184,11 @@ void vtime_account_irq_enter(struct task_struct *tsk)
         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 - ti->system_timer;
         S390_lowcore.steal_timer -= system;
         ti->system_timer = S390_lowcore.system_timer;