On 01/16/2013 11:31 AM, Rusty Russell wrote:
> Wanlong Gao <gaowanlong@xxxxxxxxxxxxxx> writes:
>> 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.
>
>> +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.
>
>> 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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