Hi Maxime,
> -----Original Message-----
> From: Maxime Coquelin <maxime.coque...@redhat.com>
> Sent: Tuesday, September 20, 2022 3:19 PM
> To: Liu, Changpeng <changpeng....@intel.com>; dev@dpdk.org
> Cc: Xia, Chenbo <chenbo....@intel.com>
> Subject: Re: [PATCH] vhost: use try_lock in rte_vhost_vring_call
>
>
>
> On 9/6/22 04:22, Changpeng Liu 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....@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 (vq_is_packed(dev))
> > vhost_vring_call_packed(dev, vq);
>
> I think that's problematic, because it will break other applications
> that currently rely on the API to block until the call is done.
>
> Just some internal DPDK usage of this API:
> ./drivers/vdpa/ifc/ifcvf_vdpa.c:871: rte_vhost_vring_call(internal->vid,
> qid);
> ./examples/vhost/virtio_net.c:236: rte_vhost_vring_call(dev->vid,
> queue_id);
> ./examples/vhost/virtio_net.c:446: rte_vhost_vring_call(dev->vid,
> queue_id);
> ./examples/vhost_blk/vhost_blk.c:99:
> rte_vhost_vring_call(task->ctrlr->vid, vq->id);
> ./examples/vhost_blk/vhost_blk.c:134:
> rte_vhost_vring_call(task->ctrlr->vid, vq->id);
>
> This change will break all the above uses.
>
> And that's not counting external projects.
>
> ou should better introduce a new API that does not block.
Could you add a new API to do this?
I think we can use the new API in SPDK as a workaround, note that SPDK project
is blocked for
a while which can't be used with DPDK 22.05 or newer.
Vhost-blk and scsi devices are not same with vhost-net, we need to cover
SeaBIOS and VM
cases, so we need to start processing vrings after 1 vring is ready.
>
> Regards,
> Maxime
