Re: irqdevice INTR example

[Christoph Hellwig <hch-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>]

On Thu, Apr 12, 2007 at 11:02:25AM +0300, Avi Kivity wrote:
> If you want condition variables, activate your cryogenically-cooled suit 
> and post on it on lkml.  This cannot be added to the kernel via kvm.

Better just rip it out.  The code would be a lot simpler with opencoded
waitqueue use, and faster aswell due to getting rid of the indirect calls.

e.g. this:

+	if (vcpu->irq.task) {
+		struct timespec tmo = {
+			.tv_sec  = 0,
+			.tv_nsec = 100000 /* 100us */
+		};
+
+		BUG_ON(vcpu->irq.task == current);
+			
+		while (vcpu->irq.task) {
+			send_sig(SIGSTOP, vcpu->irq.task, 0);
+			condvar_wait(&vcpu->irq.cv, &vcpu->irq.lock,
+				     timespec_to_jiffies(&tmo));
+		}
+		
+		vcpu->irq.pending = 1;
+	}
+	

would simply become

	if (vcpu->irq.task) {
		struct timespec tmo = {
			.tv_sec  = 0,
			.tv_nsec = 100000 /* 100us */
		};

		BUG_ON(vcpu->irq.task == current);
	
		for (;;) {
			send_sig(SIGSTOP, vcpu->irq.task, 0);
			prepare_to_wait(&vcpu->irq.wq, &wait,
					TASK_UNINTERRUPTIBLE);
			if (!vcpu->irq.task)
				break;
			spin_unlock(&vcpu->irq.lock);
			schedule_timeout(timespec_to_jiffies(&tmo));
			spin_lock(&vcpu->irq.lock);
		}
		finish_wait(&vcpu->irq.wq, &wait, TASK_UNINTERRUPTIBLE);

		vcpu->irq.pending = 1;
	}

with equal behaviour.  although the send_sig in the loop and the very short
sleep time still look rather odd to me.



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