sched: affine sync wakeups

make sync wakeups affine for cache-cold tasks: if a cache-cold task
is woken up by a sync wakeup then use the opportunity to migrate it
straight away. (the two tasks are 'related' because they communicate)

Signed-off-by: Ingo Molnar <mingo@elte.hu>

fs/pipe.c

@@ -382,7 +382,7 @@ pipe_read(struct kiocb *iocb, const struct iovec *_iov,
 
 	/* Signal writers asynchronously that there is more room. */
 	if (do_wakeup) {
-		wake_up_interruptible(&pipe->wait);
+		wake_up_interruptible_sync(&pipe->wait);
 		kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
 	}
 	if (ret > 0)
@@ -555,7 +555,7 @@ pipe_write(struct kiocb *iocb, const struct iovec *_iov,
 out:
 	mutex_unlock(&inode->i_mutex);
 	if (do_wakeup) {
-		wake_up_interruptible(&pipe->wait);
+		wake_up_interruptible_sync(&pipe->wait);
 		kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
 	}
 	if (ret > 0)
@@ -649,7 +649,7 @@ pipe_release(struct inode *inode, int decr, int decw)
 	if (!pipe->readers && !pipe->writers) {
 		free_pipe_info(inode);
 	} else {
-		wake_up_interruptible(&pipe->wait);
+		wake_up_interruptible_sync(&pipe->wait);
 		kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
 		kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
 	}

kernel/sched.c

@@ -1521,6 +1521,12 @@ static int try_to_wake_up(struct task_struct *p, unsigned int state, int sync)
 			unsigned long tl = this_load;
 			unsigned long tl_per_task;
 
+			/*
+			 * Attract cache-cold tasks on sync wakeups:
+			 */
+			if (sync && !task_hot(p, rq->clock, this_sd))
+				goto out_set_cpu;
+
 			schedstat_inc(p, se.nr_wakeups_affine_attempts);
 			tl_per_task = cpu_avg_load_per_task(this_cpu);
 
@@ -1598,7 +1604,7 @@ static int try_to_wake_up(struct task_struct *p, unsigned int state, int sync)
 	 * the waker guarantees that the freshly woken up task is going
 	 * to be considered on this CPU.)
 	 */
-	if (!sync || cpu != this_cpu)
+	if (!sync || rq->curr == rq->idle)
 		check_preempt_curr(rq, p);
 	success = 1;
 

net/unix/af_unix.c

@@ -334,7 +334,7 @@ static void unix_write_space(struct sock *sk)
 	read_lock(&sk->sk_callback_lock);
 	if (unix_writable(sk)) {
 		if (sk->sk_sleep && waitqueue_active(sk->sk_sleep))
-			wake_up_interruptible(sk->sk_sleep);
+			wake_up_interruptible_sync(sk->sk_sleep);
 		sk_wake_async(sk, 2, POLL_OUT);
 	}
 	read_unlock(&sk->sk_callback_lock);
@@ -1639,7 +1639,7 @@ static int unix_dgram_recvmsg(struct kiocb *iocb, struct socket *sock,
 	if (!skb)
 		goto out_unlock;
 
-	wake_up_interruptible(&u->peer_wait);
+	wake_up_interruptible_sync(&u->peer_wait);
 
 	if (msg->msg_name)
 		unix_copy_addr(msg, skb->sk);