Re: [PATCH] vhost: use try_lock in rte_vhost_vring_call

[Stephen Hemminger <stephen@networkplumber.org>]

On Tue,  6 Sep 2022 10:22:25 +0800
Changpeng Liu <changpeng.liu@intel.com> wrote:

> Note that this function is in data path, so the thread context
> may not same as socket messages processing context, by using
> try_lock here, users can have another try in case of VQ's access
> lock is held by `vhost-events` thread.
> 
> Signed-off-by: Changpeng Liu <changpeng.liu@intel.com>
> ---
>  lib/vhost/vhost.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/lib/vhost/vhost.c b/lib/vhost/vhost.c
> index 60cb05a0ff..072d2acb7b 100644
> --- a/lib/vhost/vhost.c
> +++ b/lib/vhost/vhost.c
> @@ -1329,7 +1329,11 @@ rte_vhost_vring_call(int vid, uint16_t vring_idx)
>  	if (!vq)
>  		return -1;
>  
> -	rte_spinlock_lock(&vq->access_lock);
> +	if (!rte_spinlock_trylock(&vq->access_lock)) {
> +		VHOST_LOG_CONFIG(dev->ifname, DEBUG,
> +			"failed to kick guest, virtqueue busy.\n");
> +		return -1;
> +	}
>  

If it is a race, logging a message is not a good idea; the log will fill
with this noise.

Instead make it statistic that can be seen by xstats.