[PATCH] vhost: use try_lock in rte_vhost_vring_call

[Liu, Changpeng]

> -----Original Message-----
> From: Stephen Hemminger <stephen at networkplumber.org>
> Sent: Wednesday, September 7, 2022 5:16 AM
> To: Liu, Changpeng <changpeng.liu at intel.com>
> Cc: dev at dpdk.org; Maxime Coquelin <maxime.coquelin at redhat.com>; Xia,
> Chenbo <chenbo.xia at intel.com>
> Subject: Re: [PATCH] vhost: use try_lock in rte_vhost_vring_call
> 
> On Tue,  6 Sep 2022 10:22:25 +0800
> Changpeng Liu <changpeng.liu at 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 at 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.
It's a DEBUG log, users can't see it in practice.