Re: [PATCH 1/3] kvm tools: Make virtio-net kvm__irq_line thread safe

[Ingo Molnar <mingo@elte.hu>]

* Asias He <asias.hejun@gmail.com> wrote:

> This patch fixes virtio-net randmom stall
> 
> host $ scp guest:/root/big.guest .
> big.guest 42%  440MB  67.7KB/s - stalled -
> 
> Signed-off-by: Asias He <asias.hejun@gmail.com>
> ---
>  tools/kvm/virtio-net.c |    9 +++++++--
>  1 files changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/kvm/virtio-net.c b/tools/kvm/virtio-net.c
> index 58b3de4..efe06cb 100644
> --- a/tools/kvm/virtio-net.c
> +++ b/tools/kvm/virtio-net.c
> @@ -77,9 +77,12 @@ static void virtio_net_rx_callback(struct kvm *self, void *param)
>  		head = virt_queue__get_iov(vq, iov, &out, &in, self);
>  		len = readv(net_device.tap_fd, iov, in);
>  		virt_queue__set_used_elem(vq, head, len);
> -	}
>  
> -	kvm__irq_line(self, VIRTIO_NET_IRQ, 1);
> +		/* We should interrupt guest right now, otherwise latency is huge. */
> +		mutex_lock(&net_device.mutex);
> +		kvm__irq_line(self, VIRTIO_NET_IRQ, 1);
> +		mutex_unlock(&net_device.mutex);
> +	}
>  }
>  
>  static void virtio_net_tx_callback(struct kvm *self, void *param)
> @@ -98,7 +101,9 @@ static void virtio_net_tx_callback(struct kvm *self, void *param)
>  		virt_queue__set_used_elem(vq, head, len);
>  	}
>  
> +	mutex_lock(&net_device.mutex);
>  	kvm__irq_line(self, VIRTIO_NET_IRQ, 1);
> +	mutex_unlock(&net_device.mutex);

I do not find this explanation adequate either. This file too could use some 
comments about how the SMP behavior looks like.

Thanks,

	Ingo