[RFC][PATCH -rt] Make futex_wait() use an hrtimer for timeout

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



  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 <[email protected]>

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 [email protected]
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

[Index of Archives]     [Kernel Newbies]     [Netfilter]     [Bugtraq]     [Photo]     [Stuff]     [Gimp]     [Yosemite News]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux RAID]     [Video 4 Linux]     [Linux for the blind]     [Linux Resources]
  Powered by Linux