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s390/vtime: correct scaled cputime of partially idle CPUs
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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>
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Martin Schwidefsky committed Sep 30, 2015
1 parent adc0b7f commit 72d38b1
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Showing 3 changed files with 67 additions and 30 deletions.
1 change: 1 addition & 0 deletions arch/s390/kernel/asm-offsets.c
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Original file line number Diff line number Diff line change
Expand Up @@ -176,6 +176,7 @@ int main(void)
DEFINE(__LC_PASTE, offsetof(struct _lowcore, paste));
DEFINE(__LC_FP_CREG_SAVE_AREA, offsetof(struct _lowcore, fpt_creg_save_area));
DEFINE(__LC_LAST_BREAK, offsetof(struct _lowcore, breaking_event_addr));
DEFINE(__LC_PERCPU_OFFSET, offsetof(struct _lowcore, percpu_offset));
DEFINE(__LC_VDSO_PER_CPU, offsetof(struct _lowcore, vdso_per_cpu_data));
DEFINE(__LC_GMAP, offsetof(struct _lowcore, gmap));
DEFINE(__LC_PGM_TDB, offsetof(struct _lowcore, pgm_tdb));
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30 changes: 29 additions & 1 deletion arch/s390/kernel/entry.S
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Original file line number Diff line number Diff line change
Expand Up @@ -733,6 +733,14 @@ ENTRY(psw_idle)
stg %r3,__SF_EMPTY(%r15)
larl %r1,.Lpsw_idle_lpsw+4
stg %r1,__SF_EMPTY+8(%r15)
#ifdef CONFIG_SMP
larl %r1,smp_cpu_mtid
llgf %r1,0(%r1)
ltgr %r1,%r1
jz .Lpsw_idle_stcctm
.insn rsy,0xeb0000000017,%r1,5,__SF_EMPTY+16(%r15)
.Lpsw_idle_stcctm:
#endif
STCK __CLOCK_IDLE_ENTER(%r2)
stpt __TIMER_IDLE_ENTER(%r2)
.Lpsw_idle_lpsw:
Expand Down Expand Up @@ -1159,7 +1167,27 @@ cleanup_critical:
jhe 1f
mvc __CLOCK_IDLE_ENTER(8,%r2),__CLOCK_IDLE_EXIT(%r2)
mvc __TIMER_IDLE_ENTER(8,%r2),__TIMER_IDLE_EXIT(%r2)
1: # account system time going idle
1: # calculate idle cycles
#ifdef CONFIG_SMP
clg %r9,BASED(.Lcleanup_idle_insn)
jl 3f
larl %r1,smp_cpu_mtid
llgf %r1,0(%r1)
ltgr %r1,%r1
jz 3f
.insn rsy,0xeb0000000017,%r1,5,__SF_EMPTY+80(%r15)
larl %r3,mt_cycles
ag %r3,__LC_PERCPU_OFFSET
la %r4,__SF_EMPTY+16(%r15)
2: lg %r0,0(%r3)
slg %r0,0(%r4)
alg %r0,64(%r4)
stg %r0,0(%r3)
la %r3,8(%r3)
la %r4,8(%r4)
brct %r1,2b
#endif
3: # account system time going idle
lg %r9,__LC_STEAL_TIMER
alg %r9,__CLOCK_IDLE_ENTER(%r2)
slg %r9,__LC_LAST_UPDATE_CLOCK
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66 changes: 37 additions & 29 deletions arch/s390/kernel/vtime.c
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Original file line number Diff line number Diff line change
Expand Up @@ -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);
Expand Down Expand Up @@ -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.
Expand All @@ -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;
Expand All @@ -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;
Expand Down Expand Up @@ -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;
Expand Down

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