Re: Performance test result between per-vhost kthread disable and enable

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Nov 23, 2010 at 10:13:43AM +0800, lidong chen wrote:
> I test the performance between per-vhost kthread disable and enable.
> 
> Test method:
> Send the same traffic load between per-vhost kthread disable and
> enable, and compare the cpu rate of host os.
> I run five vm on kvm, each of them have five nic.
> the vhost version which per-vhost kthread disable we used is rhel6
> beta 2(2.6.32.60).
> the vhost version which per-vhost kthread enable we used is rhel6 (2.6.32-71).
> 
> Test result:
> with per-vhost kthread disable, the cpu rate of host os is 110%.
> with per-vhost kthread enable, the cpu rate of host os is 130%.

Does it help if we schedule out the thread once we've passed
once over all vqs?

Something like this:

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 1b0a20d..256e915 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -175,6 +175,7 @@ static int vhost_worker(void *data)
 	struct vhost_dev *dev = data;
 	struct vhost_work *work = NULL;
 	unsigned uninitialized_var(seq);
+	int n = 0;
 
 	use_mm(dev->mm);
 
@@ -206,9 +207,11 @@ static int vhost_worker(void *data)
 		if (work) {
 			__set_current_state(TASK_RUNNING);
 			work->fn(work);
-		} else
-			schedule();
-
+			if (likely(++n < dev->nvqs))
+				continue;
+		}
+		schedule();
+		n = 0;
 	}
 	unuse_mm(dev->mm);
 	return 0;