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timerfd: Manage cancelable timers in timerfd
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Peter is concerned about the extra scan of CLOCK_REALTIME_COS in the
timer interrupt. Yes, I did not think about it, because the solution
was so elegant. I didn't like the extra list in timerfd when it was
proposed some time ago, but with a rcu based list the list walk it's
less horrible than the original global lock, which was held over the
list iteration.

Requested-by: Peter Zijlstra <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Reviewed-by: Peter Zijlstra <[email protected]>
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@KAGA-KOKO
KAGA-KOKO committed May 23, 2011
1 parent 250f972 commit 9ec2690
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Showing 5 changed files with 113 additions and 102 deletions.
105 changes: 74 additions & 31 deletions fs/timerfd.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -22,6 +22,7 @@
#include <linux/anon_inodes.h>
#include <linux/timerfd.h>
#include <linux/syscalls.h>
#include <linux/rcupdate.h>

struct timerfd_ctx {
struct hrtimer tmr;
Expand All @@ -31,9 +32,14 @@ struct timerfd_ctx {
u64 ticks;
int expired;
int clockid;
struct rcu_head rcu;
struct list_head clist;
bool might_cancel;
};

static LIST_HEAD(cancel_list);
static DEFINE_SPINLOCK(cancel_lock);

/*
* This gets called when the timer event triggers. We set the "expired"
* flag, but we do not re-arm the timer (in case it's necessary,
Expand All @@ -53,28 +59,69 @@ static enum hrtimer_restart timerfd_tmrproc(struct hrtimer *htmr)
return HRTIMER_NORESTART;
}

static ktime_t timerfd_get_remaining(struct timerfd_ctx *ctx)
/*
* Called when the clock was set to cancel the timers in the cancel
* list.
*/
void timerfd_clock_was_set(void)
{
ktime_t remaining;
ktime_t moffs = ktime_get_monotonic_offset();
struct timerfd_ctx *ctx;
unsigned long flags;

remaining = hrtimer_expires_remaining(&ctx->tmr);
return remaining.tv64 < 0 ? ktime_set(0, 0): remaining;
rcu_read_lock();
list_for_each_entry_rcu(ctx, &cancel_list, clist) {
if (!ctx->might_cancel)
continue;
spin_lock_irqsave(&ctx->wqh.lock, flags);
if (ctx->moffs.tv64 != moffs.tv64) {
ctx->moffs.tv64 = KTIME_MAX;
wake_up_locked(&ctx->wqh);
}
spin_unlock_irqrestore(&ctx->wqh.lock, flags);
}
rcu_read_unlock();
}

static bool timerfd_canceled(struct timerfd_ctx *ctx)
static void timerfd_remove_cancel(struct timerfd_ctx *ctx)
{
ktime_t moffs;
if (ctx->might_cancel) {
ctx->might_cancel = false;
spin_lock(&cancel_lock);
list_del_rcu(&ctx->clist);
spin_unlock(&cancel_lock);
}
}

if (!ctx->might_cancel)
static bool timerfd_canceled(struct timerfd_ctx *ctx)
{
if (!ctx->might_cancel || ctx->moffs.tv64 != KTIME_MAX)
return false;
ctx->moffs = ktime_get_monotonic_offset();
return true;
}

moffs = ktime_get_monotonic_offset();
static void timerfd_setup_cancel(struct timerfd_ctx *ctx, int flags)
{
if (ctx->clockid == CLOCK_REALTIME && (flags & TFD_TIMER_ABSTIME) &&
(flags & TFD_TIMER_CANCEL_ON_SET)) {
if (!ctx->might_cancel) {
ctx->might_cancel = true;
spin_lock(&cancel_lock);
list_add_rcu(&ctx->clist, &cancel_list);
spin_unlock(&cancel_lock);
}
} else if (ctx->might_cancel) {
timerfd_remove_cancel(ctx);
}
}

if (moffs.tv64 == ctx->moffs.tv64)
return false;
static ktime_t timerfd_get_remaining(struct timerfd_ctx *ctx)
{
ktime_t remaining;

ctx->moffs = moffs;
return true;
remaining = hrtimer_expires_remaining(&ctx->tmr);
return remaining.tv64 < 0 ? ktime_set(0, 0): remaining;
}

static int timerfd_setup(struct timerfd_ctx *ctx, int flags,
Expand All @@ -87,13 +134,6 @@ static int timerfd_setup(struct timerfd_ctx *ctx, int flags,
htmode = (flags & TFD_TIMER_ABSTIME) ?
HRTIMER_MODE_ABS: HRTIMER_MODE_REL;

ctx->might_cancel = false;
if (htmode == HRTIMER_MODE_ABS && ctx->clockid == CLOCK_REALTIME &&
(flags & TFD_TIMER_CANCELON_SET)) {
clockid = CLOCK_REALTIME_COS;
ctx->might_cancel = true;
}

texp = timespec_to_ktime(ktmr->it_value);
ctx->expired = 0;
ctx->ticks = 0;
Expand All @@ -113,8 +153,9 @@ static int timerfd_release(struct inode *inode, struct file *file)
{
struct timerfd_ctx *ctx = file->private_data;

timerfd_remove_cancel(ctx);
hrtimer_cancel(&ctx->tmr);
kfree(ctx);
kfree_rcu(ctx, rcu);
return 0;
}

Expand Down Expand Up @@ -149,20 +190,20 @@ static ssize_t timerfd_read(struct file *file, char __user *buf, size_t count,
else
res = wait_event_interruptible_locked_irq(ctx->wqh, ctx->ticks);

/*
* If clock has changed, we do not care about the
* ticks and we do not rearm the timer. Userspace must
* reevaluate anyway.
*/
if (timerfd_canceled(ctx)) {
ctx->ticks = 0;
ctx->expired = 0;
res = -ECANCELED;
}

if (ctx->ticks) {
ticks = ctx->ticks;

/*
* If clock has changed, we do not care about the
* ticks and we do not rearm the timer. Userspace must
* reevaluate anyway.
*/
if (timerfd_canceled(ctx)) {
ticks = 0;
ctx->expired = 0;
res = -ECANCELED;
}

if (ctx->expired && ctx->tintv.tv64) {
/*
* If tintv.tv64 != 0, this is a periodic timer that
Expand Down Expand Up @@ -258,6 +299,8 @@ SYSCALL_DEFINE4(timerfd_settime, int, ufd, int, flags,
return PTR_ERR(file);
ctx = file->private_data;

timerfd_setup_cancel(ctx, flags);

/*
* We need to stop the existing timer before reprogramming
* it to the new values.
Expand Down
6 changes: 5 additions & 1 deletion include/linux/hrtimer.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -155,7 +155,6 @@ enum hrtimer_base_type {
HRTIMER_BASE_REALTIME,
HRTIMER_BASE_MONOTONIC,
HRTIMER_BASE_BOOTTIME,
HRTIMER_BASE_REALTIME_COS,
HRTIMER_MAX_CLOCK_BASES,
};

Expand Down Expand Up @@ -306,6 +305,11 @@ static inline int hrtimer_is_hres_active(struct hrtimer *timer)
#endif

extern void clock_was_set(void);
#ifdef CONFIG_TIMERFD
extern void timerfd_clock_was_set(void);
#else
static inline void timerfd_clock_was_set(void) { }
#endif
extern void hrtimers_resume(void);

extern ktime_t ktime_get(void);
Expand Down
6 changes: 0 additions & 6 deletions include/linux/time.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -302,12 +302,6 @@ struct itimerval {
* The IDs of various hardware clocks:
*/
#define CLOCK_SGI_CYCLE 10

#ifdef __KERNEL__
/* This clock is not exposed to user space */
#define CLOCK_REALTIME_COS 15
#endif

#define MAX_CLOCKS 16
#define CLOCKS_MASK (CLOCK_REALTIME | CLOCK_MONOTONIC)
#define CLOCKS_MONO CLOCK_MONOTONIC
Expand Down
4 changes: 2 additions & 2 deletions include/linux/timerfd.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -19,14 +19,14 @@
* shared O_* flags.
*/
#define TFD_TIMER_ABSTIME (1 << 0)
#define TFD_TIMER_CANCELON_SET (1 << 1)
#define TFD_TIMER_CANCEL_ON_SET (1 << 1)
#define TFD_CLOEXEC O_CLOEXEC
#define TFD_NONBLOCK O_NONBLOCK

#define TFD_SHARED_FCNTL_FLAGS (TFD_CLOEXEC | TFD_NONBLOCK)
/* Flags for timerfd_create. */
#define TFD_CREATE_FLAGS TFD_SHARED_FCNTL_FLAGS
/* Flags for timerfd_settime. */
#define TFD_SETTIME_FLAGS (TFD_TIMER_ABSTIME | TFD_TIMER_CANCELON_SET)
#define TFD_SETTIME_FLAGS (TFD_TIMER_ABSTIME | TFD_TIMER_CANCEL_ON_SET)

#endif /* _LINUX_TIMERFD_H */
94 changes: 32 additions & 62 deletions kernel/hrtimer.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -78,19 +78,13 @@ DEFINE_PER_CPU(struct hrtimer_cpu_base, hrtimer_bases) =
.get_time = &ktime_get_boottime,
.resolution = KTIME_LOW_RES,
},
{
.index = CLOCK_REALTIME_COS,
.get_time = &ktime_get_real,
.resolution = KTIME_LOW_RES,
},
}
};

static const int hrtimer_clock_to_base_table[MAX_CLOCKS] = {
[CLOCK_REALTIME] = HRTIMER_BASE_REALTIME,
[CLOCK_MONOTONIC] = HRTIMER_BASE_MONOTONIC,
[CLOCK_BOOTTIME] = HRTIMER_BASE_BOOTTIME,
[CLOCK_REALTIME_COS] = HRTIMER_BASE_REALTIME_COS,
};

static inline int hrtimer_clockid_to_base(clockid_t clock_id)
Expand All @@ -116,7 +110,6 @@ static void hrtimer_get_softirq_time(struct hrtimer_cpu_base *base)
base->clock_base[HRTIMER_BASE_REALTIME].softirq_time = xtim;
base->clock_base[HRTIMER_BASE_MONOTONIC].softirq_time = mono;
base->clock_base[HRTIMER_BASE_BOOTTIME].softirq_time = boot;
base->clock_base[HRTIMER_BASE_REALTIME_COS].softirq_time = xtim;
}

/*
Expand Down Expand Up @@ -486,8 +479,6 @@ static inline void debug_deactivate(struct hrtimer *timer)
trace_hrtimer_cancel(timer);
}

static void hrtimer_expire_cancelable(struct hrtimer_cpu_base *cpu_base);

/* High resolution timer related functions */
#ifdef CONFIG_HIGH_RES_TIMERS

Expand Down Expand Up @@ -663,7 +654,33 @@ static inline int hrtimer_enqueue_reprogram(struct hrtimer *timer,
return 0;
}

static void retrigger_next_event(void *arg);
/*
* Retrigger next event is called after clock was set
*
* Called with interrupts disabled via on_each_cpu()
*/
static void retrigger_next_event(void *arg)
{
struct hrtimer_cpu_base *base = &__get_cpu_var(hrtimer_bases);
struct timespec realtime_offset, xtim, wtm, sleep;

if (!hrtimer_hres_active())
return;

/* Optimized out for !HIGH_RES */
get_xtime_and_monotonic_and_sleep_offset(&xtim, &wtm, &sleep);
set_normalized_timespec(&realtime_offset, -wtm.tv_sec, -wtm.tv_nsec);

/* Adjust CLOCK_REALTIME offset */
raw_spin_lock(&base->lock);
base->clock_base[HRTIMER_BASE_REALTIME].offset =
timespec_to_ktime(realtime_offset);
base->clock_base[HRTIMER_BASE_BOOTTIME].offset =
timespec_to_ktime(sleep);

hrtimer_force_reprogram(base, 0);
raw_spin_unlock(&base->lock);
}

/*
* Switch to high resolution mode
Expand Down Expand Up @@ -711,45 +728,10 @@ static inline int hrtimer_enqueue_reprogram(struct hrtimer *timer,
return 0;
}
static inline void hrtimer_init_hres(struct hrtimer_cpu_base *base) { }
static inline void retrigger_next_event(void *arg) { }

#endif /* CONFIG_HIGH_RES_TIMERS */

/*
* Retrigger next event is called after clock was set
*
* Called with interrupts disabled via on_each_cpu()
*/
static void retrigger_next_event(void *arg)
{
struct hrtimer_cpu_base *base = &__get_cpu_var(hrtimer_bases);
struct timespec realtime_offset, xtim, wtm, sleep;

if (!hrtimer_hres_active()) {
raw_spin_lock(&base->lock);
hrtimer_expire_cancelable(base);
raw_spin_unlock(&base->lock);
return;
}

/* Optimized out for !HIGH_RES */
get_xtime_and_monotonic_and_sleep_offset(&xtim, &wtm, &sleep);
set_normalized_timespec(&realtime_offset, -wtm.tv_sec, -wtm.tv_nsec);

/* Adjust CLOCK_REALTIME offset */
raw_spin_lock(&base->lock);
base->clock_base[HRTIMER_BASE_REALTIME].offset =
timespec_to_ktime(realtime_offset);
base->clock_base[HRTIMER_BASE_BOOTTIME].offset =
timespec_to_ktime(sleep);
base->clock_base[HRTIMER_BASE_REALTIME_COS].offset =
timespec_to_ktime(realtime_offset);

hrtimer_expire_cancelable(base);

hrtimer_force_reprogram(base, 0);
raw_spin_unlock(&base->lock);
}

/*
* Clock realtime was set
*
Expand All @@ -763,8 +745,11 @@ static void retrigger_next_event(void *arg)
*/
void clock_was_set(void)
{
#ifdef CONFIG_HIGHRES_TIMERS
/* Retrigger the CPU local events everywhere */
on_each_cpu(retrigger_next_event, NULL, 1);
#endif
timerfd_clock_was_set();
}

/*
Expand All @@ -777,6 +762,7 @@ void hrtimers_resume(void)
KERN_INFO "hrtimers_resume() called with IRQs enabled!");

retrigger_next_event(NULL);
timerfd_clock_was_set();
}

static inline void timer_stats_hrtimer_set_start_info(struct hrtimer *timer)
Expand Down Expand Up @@ -1240,22 +1226,6 @@ static void __run_hrtimer(struct hrtimer *timer, ktime_t *now)
timer->state &= ~HRTIMER_STATE_CALLBACK;
}

static void hrtimer_expire_cancelable(struct hrtimer_cpu_base *cpu_base)
{
struct timerqueue_node *node;
struct hrtimer_clock_base *base;
ktime_t now = ktime_get_real();

base = &cpu_base->clock_base[HRTIMER_BASE_REALTIME_COS];

while ((node = timerqueue_getnext(&base->active))) {
struct hrtimer *timer;

timer = container_of(node, struct hrtimer, node);
__run_hrtimer(timer, &now);
}
}

#ifdef CONFIG_HIGH_RES_TIMERS

/*
Expand Down

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