On 01/16/2013 11:31 AM, Rusty Russell wrote:

Wanlong Gao [off-list ref] writes:

quoted

Add hot cpu notifier to reset the request virtqueue affinity
when doing cpu hotplug.

You need to be careful to get_online_cpus() and put_online_cpus() here,
so CPUs can't go up and down in the middle of operations.

In particular, get_online_cpus()/put_online_cpus() around calls to
virtscsi_set_affinity() (except within notifiers).

Yes, I'll take care of this, thank you.

quoted

+static int virtscsi_cpu_callback(struct notifier_block *nfb,
+				 unsigned long action, void *hcpu)
+{
+	struct virtio_scsi *vscsi = container_of(nfb, struct virtio_scsi, nb);
+	switch(action) {
+	case CPU_ONLINE:
+	case CPU_ONLINE_FROZEN:
+	case CPU_DEAD:
+	case CPU_DEAD_FROZEN:
+		virtscsi_set_affinity(vscsi, true);
+		break;
+	default:
+		break;
+	}
+	return NOTIFY_OK;
+}

You probably want to remove affinities *before* the CPU goes down, and
restore it after the CPU comes up.

So, how about:

        switch (action & ~CPU_TASKS_FROZEN) {
        case CPU_ONLINE:
        case CPU_DOWN_FAILED:
                virtscsi_set_affinity(vscsi, true, -1);
                break;
        case CPU_DOWN_PREPARE:
                virtscsi_set_affinity(vscsi, true, (unsigned long)hcpu);
                break;
        }

The extra argument to virtscsi_set_affinity() is to tell it to ignore a
cpu which seems online (because it's going down).

OK, thank you very much for teaching this.

quoted

 static void virtscsi_init_vq(struct virtio_scsi_vq *virtscsi_vq,
 			     struct virtqueue *vq)
 {

@@ -888,6 +909,13 @@ static int __devinit virtscsi_probe(struct virtio_device *vdev)
 	if (err)
 		goto virtscsi_init_failed;
 
+	vscsi->nb.notifier_call = &virtscsi_cpu_callback;
+	err = register_hotcpu_notifier(&vscsi->nb);
+	if (err) {
+		pr_err("virtio_scsi: registering cpu notifier failed\n");
+		goto scsi_add_host_failed;
+	}
+

You have to clean this up if scsi_add_host() fails, I think.

Yeah, will do, thank you very much. 


Regards,
Wanlong Gao

Cheers,
Rusty.
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