[PATCH RFC] hrtimers: add slop parameter

From: Rusty Russell
Date: Tue Dec 18 2007 - 02:28:19 EST

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(I don't really like this patch yet, but wanted to get something out there)

After discussion with Thomas Gleixner, we came up with the idea of
introducing a new parameter to hrtimers (and probably eventually all
timers in the kernel, then onto userspace). I call it "slop", and it
is an indication of how precise a timer should be.

The idea is that this "slop" can be used to calculate what timers can
be batched, and maybe even eventually unify normal and high res timers.
A timer should fire no earlier than its expiry, but we don't care if it's
delayed until after expiry+slop.

For this patch, DEFAULT_SLOP (currently 0) is used everywhere, and
the parameter is unused.

diff -r 0eabf082c13a drivers/kvm/lapic.c
--- a/drivers/kvm/lapic.c Tue Dec 18 13:51:13 2007 +1100
+++ b/drivers/kvm/lapic.c Tue Dec 18 15:04:33 2007 +1100
@@ -968,7 +968,8 @@ int kvm_create_lapic(struct kvm_vcpu *vc
memset(apic->regs, 0, PAGE_SIZE);
apic->vcpu = vcpu;

- hrtimer_init(&apic->timer.dev, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
+ hrtimer_init(&apic->timer.dev, CLOCK_MONOTONIC, HRTIMER_MODE_ABS,
+ DEFAULT_SLOP);
apic->timer.dev.function = apic_timer_fn;
apic->base_address = APIC_DEFAULT_PHYS_BASE;
vcpu->apic_base = APIC_DEFAULT_PHYS_BASE;
diff -r 0eabf082c13a drivers/net/virtio_net.c
--- a/drivers/net/virtio_net.c Tue Dec 18 13:51:13 2007 +1100
+++ b/drivers/net/virtio_net.c Tue Dec 18 15:04:33 2007 +1100
@@ -403,7 +403,8 @@ static int virtnet_probe(struct virtio_d
netif_napi_add(dev, &vi->napi, virtnet_poll, 16);
vi->dev = dev;
vi->vdev = vdev;
- hrtimer_init(&vi->tx_timer, CLOCK_REALTIME, HRTIMER_MODE_REL);
+ hrtimer_init(&vi->tx_timer, CLOCK_REALTIME, HRTIMER_MODE_REL,
+ DEFAULT_SLOP);
vi->tx_timer.function = kick_xmit;
vi->tx_timer.cb_mode = HRTIMER_CB_SOFTIRQ;
vi->out_max = -1U;
diff -r 0eabf082c13a include/linux/hrtimer.h
--- a/include/linux/hrtimer.h Tue Dec 18 13:51:13 2007 +1100
+++ b/include/linux/hrtimer.h Tue Dec 18 15:04:33 2007 +1100
@@ -100,6 +100,7 @@ enum hrtimer_cb_mode {
* @cb_mode: high resolution timer feature to select the callback execution
* mode
* @cb_entry: list head to enqueue an expired timer into the callback list
+ * @slop: how much extra delay can be added (eg. for deferring wakeups)
* @start_site: timer statistics field to store the site where the timer
* was started
* @start_comm: timer statistics field to store the name of the process which
@@ -118,6 +119,7 @@ struct hrtimer {
#ifdef CONFIG_HIGH_RES_TIMERS
enum hrtimer_cb_mode cb_mode;
struct list_head cb_entry;
+ ktime_t slop;
#endif
#ifdef CONFIG_TIMER_STATS
void *start_site;
@@ -256,8 +258,9 @@ extern ktime_t ktime_get_real(void);
/* Exported timer functions: */

/* Initialize timers: */
+#define DEFAULT_SLOP ((ktime_t) { .tv64 = 0 })
extern void hrtimer_init(struct hrtimer *timer, clockid_t which_clock,
- enum hrtimer_mode mode);
+ enum hrtimer_mode mode, ktime_t slop);

/* Basic timer operations: */
extern int hrtimer_start(struct hrtimer *timer, ktime_t tim,
diff -r 0eabf082c13a kernel/fork.c
--- a/kernel/fork.c Tue Dec 18 13:51:13 2007 +1100
+++ b/kernel/fork.c Tue Dec 18 15:04:33 2007 +1100
@@ -874,7 +874,8 @@ static int copy_signal(unsigned long clo
init_sigpending(&sig->shared_pending);
INIT_LIST_HEAD(&sig->posix_timers);

- hrtimer_init(&sig->real_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
+ hrtimer_init(&sig->real_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL,
+ DEFAULT_SLOP);
sig->it_real_incr.tv64 = 0;
sig->real_timer.function = it_real_fn;
sig->tsk = tsk;
diff -r 0eabf082c13a kernel/futex.c
--- a/kernel/futex.c Tue Dec 18 13:51:13 2007 +1100
+++ b/kernel/futex.c Tue Dec 18 15:04:33 2007 +1100
@@ -1247,7 +1247,8 @@ static int futex_wait(u32 __user *uaddr,
if (!abs_time)
schedule();
else {
- hrtimer_init(&t.timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
+ hrtimer_init(&t.timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS,
+ DEFAULT_SLOP);
hrtimer_init_sleeper(&t, current);
t.timer.expires = *abs_time;

@@ -1344,7 +1345,8 @@ static int futex_lock_pi(u32 __user *uad

if (time) {
to = &timeout;
- hrtimer_init(&to->timer, CLOCK_REALTIME, HRTIMER_MODE_ABS);
+ hrtimer_init(&to->timer, CLOCK_REALTIME, HRTIMER_MODE_ABS,
+ DEFAULT_SLOP);
hrtimer_init_sleeper(to, current);
to->timer.expires = *time;
}
diff -r 0eabf082c13a kernel/hrtimer.c
--- a/kernel/hrtimer.c Tue Dec 18 13:51:13 2007 +1100
+++ b/kernel/hrtimer.c Tue Dec 18 15:04:33 2007 +1100
@@ -522,9 +522,10 @@ static inline void hrtimer_init_hres(str
/*
* Initialize the high resolution related parts of a hrtimer
*/
-static inline void hrtimer_init_timer_hres(struct hrtimer *timer)
+static inline void hrtimer_init_timer_hres(struct hrtimer *timer, ktime_t slop)
{
INIT_LIST_HEAD(&timer->cb_entry);
+ timer->slop = slop;
}

/*
@@ -621,7 +622,9 @@ static inline int hrtimer_cb_pending(str
static inline int hrtimer_cb_pending(struct hrtimer *timer) { return 0; }
static inline void hrtimer_remove_cb_pending(struct hrtimer *timer) { }
static inline void hrtimer_init_hres(struct hrtimer_cpu_base *base) { }
-static inline void hrtimer_init_timer_hres(struct hrtimer *timer) { }
+static inline void hrtimer_init_timer_hres(struct hrtimer *timer, ktime_t slop)
+{
+}

#endif /* CONFIG_HIGH_RES_TIMERS */

@@ -987,9 +990,10 @@ ktime_t hrtimer_get_next_event(void)
* @timer: the timer to be initialized
* @clock_id: the clock to be used
* @mode: timer mode abs/rel
+ * @slop: delay which can be added to timer without significant effect.
*/
void hrtimer_init(struct hrtimer *timer, clockid_t clock_id,
- enum hrtimer_mode mode)
+ enum hrtimer_mode mode, ktime_t slop)
{
struct hrtimer_cpu_base *cpu_base;

@@ -1001,7 +1005,7 @@ void hrtimer_init(struct hrtimer *timer,
clock_id = CLOCK_MONOTONIC;

timer->base = &cpu_base->clock_base[clock_id];
- hrtimer_init_timer_hres(timer);
+ hrtimer_init_timer_hres(timer, slop);

#ifdef CONFIG_TIMER_STATS
timer->start_site = NULL;
@@ -1299,7 +1303,7 @@ long __sched hrtimer_nanosleep_restart(s

restart->fn = do_no_restart_syscall;

- hrtimer_init(&t.timer, restart->arg0, HRTIMER_MODE_ABS);
+ hrtimer_init(&t.timer, restart->arg0, HRTIMER_MODE_ABS, DEFAULT_SLOP);
t.timer.expires.tv64 = ((u64)restart->arg3 << 32) | (u64) restart->arg2;

if (do_nanosleep(&t, HRTIMER_MODE_ABS))
@@ -1326,7 +1330,7 @@ long hrtimer_nanosleep(struct timespec *
struct hrtimer_sleeper t;
ktime_t rem;

- hrtimer_init(&t.timer, clockid, mode);
+ hrtimer_init(&t.timer, clockid, mode, DEFAULT_SLOP);
t.timer.expires = timespec_to_ktime(*rqtp);
if (do_nanosleep(&t, mode))
return 0;
diff -r 0eabf082c13a kernel/posix-timers.c
--- a/kernel/posix-timers.c Tue Dec 18 13:51:13 2007 +1100
+++ b/kernel/posix-timers.c Tue Dec 18 15:04:33 2007 +1100
@@ -194,7 +194,8 @@ static inline int common_clock_set(const

static int common_timer_create(struct k_itimer *new_timer)
{
- hrtimer_init(&new_timer->it.real.timer, new_timer->it_clock, 0);
+ hrtimer_init(&new_timer->it.real.timer, new_timer->it_clock, 0,
+ DEFAULT_SLOP);
return 0;
}

@@ -755,7 +756,7 @@ common_timer_set(struct k_itimer *timr,
return 0;

mode = flags & TIMER_ABSTIME ? HRTIMER_MODE_ABS : HRTIMER_MODE_REL;
- hrtimer_init(&timr->it.real.timer, timr->it_clock, mode);
+ hrtimer_init(&timr->it.real.timer, timr->it_clock, mode, DEFAULT_SLOP);
timr->it.real.timer.function = posix_timer_fn;

timer->expires = timespec_to_ktime(new_setting->it_value);
diff -r 0eabf082c13a kernel/time/tick-sched.c
--- a/kernel/time/tick-sched.c Tue Dec 18 13:51:13 2007 +1100
+++ b/kernel/time/tick-sched.c Tue Dec 18 15:04:33 2007 +1100
@@ -475,7 +475,8 @@ static void tick_nohz_switch_to_nohz(voi
* Recycle the hrtimer in ts, so we can share the
* hrtimer_forward with the highres code.
*/
- hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
+ hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS,
+ DEFAULT_SLOP);
/* Get the next period */
next = tick_init_jiffy_update();

@@ -579,7 +580,8 @@ void tick_setup_sched_timer(void)
/*
* Emulate tick processing via per-CPU hrtimers:
*/
- hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
+ hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS,
+ DEFAULT_SLOP);
ts->sched_timer.function = tick_sched_timer;
ts->sched_timer.cb_mode = HRTIMER_CB_IRQSAFE_NO_SOFTIRQ;

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Next message: Pekka J Enberg: "Re: [RFC/PATCH 2/8] revoke: inode revoke lock V7"
Previous message: Rusty Russell: "Re: [RFC] [patch 1/2] add non_init_kernel_text_address"
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