Re: [dpdk-dev] [PATCH] vhost_user: protect active rings from async ring changes

[Yuanhan Liu <yliu@fridaylinux.org>]

On Wed, Dec 06, 2017 at 03:55:49PM +0200, Victor Kaplansky wrote:
> When performing live migration or memory hot-plugging,
> the changes to the device and vrings made by message handler
> done independently from vring usage by PMD threads.
> 
> This causes for example segfauls during live-migration
> with MQ enable, but in general virtually any request
> sent by qemu changing the state of device can cause
> problems.
> 
> These patches fixes all above issues by adding a spinlock
> to every vring and requiring message handler to start operation
> only after ensuring that all PMD threads related to the divece
> are out of critical section accessing the vring data.
> 
> Each vring has its own lock in order to not create contention
> between PMD threads of different vrings and to prevent
> performance degradation by scaling queue pair number.

Hi,

Thanks for the patch! Firstly, I didn't see your SoB.

I'm also more interested to know do you see any performance penalty?

> ---
>  lib/librte_vhost/vhost.h      |  1 +
>  lib/librte_vhost/vhost_user.c | 44 +++++++++++++++++++++++++++++++++++++++++++
>  lib/librte_vhost/virtio_net.c |  8 ++++++++
>  3 files changed, 53 insertions(+)
> 
> diff --git a/lib/librte_vhost/vhost.h b/lib/librte_vhost/vhost.h
> index 1cc81c17..812aeccd 100644
> --- a/lib/librte_vhost/vhost.h
> +++ b/lib/librte_vhost/vhost.h
> @@ -137,6 +137,7 @@ struct vhost_virtqueue {
>  	TAILQ_HEAD(, vhost_iotlb_entry) iotlb_list;
>  	int				iotlb_cache_nr;
>  	TAILQ_HEAD(, vhost_iotlb_entry) iotlb_pending_list;
> +        rte_spinlock_t active_lock;

The indentation is broken.

>  } __rte_cache_aligned;
> @@ -1356,6 +1361,8 @@ rte_vhost_dequeue_burst(int vid, uint16_t queue_id,
>  	if (dev->features & (1ULL << VIRTIO_F_IOMMU_PLATFORM))
>  		vhost_user_iotlb_rd_unlock(vq);
>  
> +        rte_spinlock_unlock(&vq->active_lock);        

Ditto.

	--yliu