Messages in this thread Patch in this message | ![/](/images/icornerl.gif) | | Date | Wed, 12 Apr 2006 11:42:43 +0200 | From | Sébastien Dugué <> | Subject | [RFC][PATCH -rt] Make futex_wait() use an hrtimer for timeout |
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Hi,
This patch modifies futex_wait() to use an hrtimer + schedule() in place of schedule_timeout() in an RT kernel.
More details in the patch header.
Sébastien.
--------------------------------------------------------------------------------
This patch modifies futex_wait() to use an hrtimer + schedule() in place of schedule_timeout().
schedule_timeout() is tick based, therefore the timeout granularity is the tick (1 ms, 4 ms or 10 ms depending on HZ). By using a high resolution timer for timeout wakeup, we can attain a much finer timeout granularity (in the microsecond range). This parallels what is already done for futex_lock_pi().
The timeout passed to the syscall is no longer converted to jiffies and is therefore passed to do_futex() and futex_wait() as a timespec therefore keeping nanosecond resolution.
Also this removes the need to pass the nanoseconds timeout part to futex_lock_pi() in val2.
In futex_wait(), if the timeout is zero then a regular schedule() is performed. Otherwise, an hrtimer is fired before schedule() is called.
include/linux/futex.h | 2 - kernel/futex.c | 56 +++++++++++++++++++++++++++++++++----------------- kernel/futex_compat.c | 9 -------- 3 files changed, 40 insertions(+), 27 deletions(-)
Signed-off-by: Sébastien Dugué <sebastien.dugue@bull.net>
Index: linux-2.6.16-rt16/include/linux/futex.h =================================================================== --- linux-2.6.16-rt16.orig/include/linux/futex.h 2006-04-12 11:20:57.000000000 +0200 +++ linux-2.6.16-rt16/include/linux/futex.h 2006-04-12 11:21:01.000000000 +0200 @@ -93,7 +93,7 @@ struct robust_list_head { */ #define ROBUST_LIST_LIMIT 2048 -long do_futex(u32 __user *uaddr, int op, u32 val, unsigned long timeout, +long do_futex(u32 __user *uaddr, int op, u32 val, struct timespec *timeout, u32 __user *uaddr2, u32 val2, u32 val3); extern int handle_futex_death(u32 __user *uaddr, struct task_struct *curr); Index: linux-2.6.16-rt16/kernel/futex.c =================================================================== --- linux-2.6.16-rt16.orig/kernel/futex.c 2006-04-12 11:20:57.000000000 +0200 +++ linux-2.6.16-rt16/kernel/futex.c 2006-04-12 11:21:01.000000000 +0200 @@ -49,6 +49,7 @@ #include <linux/syscalls.h> #include <linux/signal.h> #include <asm/futex.h> +#include <linux/hrtimer.h> #include "rtmutex_common.h" @@ -968,7 +969,7 @@ static void unqueue_me_pi(struct futex_q drop_key_refs(&q->key); } -static int futex_wait(u32 __user *uaddr, u32 val, unsigned long time) +static int futex_wait(u32 __user *uaddr, u32 val, struct timespec *time) { struct task_struct *curr = current; DECLARE_WAITQUEUE(wait, curr); @@ -976,6 +977,8 @@ static int futex_wait(u32 __user *uaddr, struct futex_q q; u32 uval; int ret; + struct hrtimer_sleeper t; + int rem = 0; q.pi_state = NULL; retry: @@ -1057,7 +1060,31 @@ static int futex_wait(u32 __user *uaddr, unsigned long nosched_flag = current->flags & PF_NOSCHED; current->flags &= ~PF_NOSCHED; - time = schedule_timeout(time); + + if (time->tv_sec == 0 && time->tv_nsec == 0) + schedule(); + else { + + hrtimer_init(&t.timer, CLOCK_MONOTONIC, HRTIMER_REL); + hrtimer_init_sleeper(&t, current); + t.timer.expires = timespec_to_ktime(*time); + + hrtimer_start(&t.timer, t.timer.expires, HRTIMER_REL); + + /* + * the timer could have already expired, in which + * case current would be flagged for rescheduling. + * Don't bother calling schedule. + */ + if (likely(t.task)) + schedule(); + + hrtimer_cancel(&t.timer); + + /* Flag if a timeout occured */ + rem = (t.task == NULL); + } + current->flags |= nosched_flag; } __set_current_state(TASK_RUNNING); @@ -1070,7 +1097,7 @@ static int futex_wait(u32 __user *uaddr, /* If we were woken (and unqueued), we succeeded, whatever. */ if (!unqueue_me(&q)) return 0; - if (time == 0) + if (rem) return -ETIMEDOUT; /* * We expect signal_pending(current), but another thread may @@ -1093,7 +1120,7 @@ static int futex_wait(u32 __user *uaddr, * races the kernel might see a 0 value of the futex too.) */ static int futex_lock_pi(u32 __user *uaddr, int detect, - unsigned long sec, long nsec, int trylock) + struct timespec *time, int trylock) { struct task_struct *curr = current; struct futex_hash_bucket *hb; @@ -1107,11 +1134,11 @@ static int futex_lock_pi(u32 __user *uad pr_debug("Futex lock pi: %d\n", current->pid); - if (sec != MAX_SCHEDULE_TIMEOUT) { + if (time->tv_sec || time->tv_nsec) { to = &timeout; hrtimer_init(&to->timer, CLOCK_REALTIME, HRTIMER_ABS); hrtimer_init_sleeper(to, current); - to->timer.expires = ktime_set(sec, nsec); + to->timer.expires = timespec_to_ktime(*time); } q.pi_state = NULL; @@ -1708,7 +1735,7 @@ void exit_robust_list(struct task_struct } } -long do_futex(u32 __user *uaddr, int op, u32 val, unsigned long timeout, +long do_futex(u32 __user *uaddr, int op, u32 val, struct timespec *timeout, u32 __user *uaddr2, u32 val2, u32 val3) { int ret; @@ -1734,13 +1761,13 @@ long do_futex(u32 __user *uaddr, int op, ret = futex_wake_op(uaddr, uaddr2, val, val2, val3); break; case FUTEX_LOCK_PI: - ret = futex_lock_pi(uaddr, val, timeout, val2, 0); + ret = futex_lock_pi(uaddr, val, timeout, 0); break; case FUTEX_UNLOCK_PI: ret = futex_unlock_pi(uaddr); break; case FUTEX_TRYLOCK_PI: - ret = futex_lock_pi(uaddr, 0, timeout, val2, 1); + ret = futex_lock_pi(uaddr, 0, timeout, 1); break; default: ret = -ENOSYS; @@ -1753,8 +1780,7 @@ asmlinkage long sys_futex(u32 __user *ua struct timespec __user *utime, u32 __user *uaddr2, u32 val3) { - struct timespec t; - unsigned long timeout = MAX_SCHEDULE_TIMEOUT; + struct timespec t = {.tv_sec=0, .tv_nsec=0}; u32 val2 = 0; if (utime && (op == FUTEX_WAIT || op == FUTEX_LOCK_PI)) { @@ -1762,12 +1788,6 @@ asmlinkage long sys_futex(u32 __user *ua return -EFAULT; if (!timespec_valid(&t)) return -EINVAL; - if (op == FUTEX_WAIT) - timeout = timespec_to_jiffies(&t) + 1; - else { - timeout = t.tv_sec; - val2 = t.tv_nsec; - } } /* * requeue parameter in 'utime' if op == FUTEX_REQUEUE. @@ -1775,7 +1795,7 @@ asmlinkage long sys_futex(u32 __user *ua if (op == FUTEX_REQUEUE || op == FUTEX_CMP_REQUEUE) val2 = (u32) (unsigned long) utime; - return do_futex(uaddr, op, val, timeout, uaddr2, val2, val3); + return do_futex(uaddr, op, val, &t, uaddr2, val2, val3); } static struct super_block * Index: linux-2.6.16-rt16/kernel/futex_compat.c =================================================================== --- linux-2.6.16-rt16.orig/kernel/futex_compat.c 2006-04-12 11:20:57.000000000 +0200 +++ linux-2.6.16-rt16/kernel/futex_compat.c 2006-04-12 11:21:01.000000000 +0200 @@ -125,8 +125,7 @@ asmlinkage long compat_sys_futex(u32 __u struct compat_timespec __user *utime, u32 __user *uaddr2, u32 val3) { - struct timespec t; - unsigned long timeout = MAX_SCHEDULE_TIMEOUT; + struct timespec t = {.tv_sec=0, .tv_nsec=0}; int val2 = 0; if (utime && (op == FUTEX_WAIT || op == FUTEX_LOCK_PI)) { @@ -134,12 +133,6 @@ asmlinkage long compat_sys_futex(u32 __u return -EFAULT; if (!timespec_valid(&t)) return -EINVAL; - if (op == FUTEX_WAIT) - timeout = timespec_to_jiffies(&t) + 1; - else { - timeout = t.tv_sec; - val2 = t.tv_nsec; - } } if (op == FUTEX_REQUEUE || op == FUTEX_CMP_REQUEUE) val2 = (int) (unsigned long) utime; - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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