Re: [RFC PATCH net-next 03/12] vhost_net: introduce vhost_has_more_pkts()

Jason Wang
2018-05-22T12:31:49Z

On 2018年05月22日 00:39, Jesse Brandeburg wrote:
> On Mon, 21 May 2018 17:04:24 +0800 Jason wrote:
>> Signed-off-by: Jason Wang <jasowang@redhat.com>
>> ---
>> drivers/vhost/net.c | 12 +++++++++---
>> 1 file changed, 9 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
>> index de544ee..4ebac76 100644
>> --- a/drivers/vhost/net.c
>> +++ b/drivers/vhost/net.c
>> @@ -485,6 +485,13 @@ static bool vhost_exceeds_weight(int pkts, int total_len)
>> unlikely(pkts >= VHOST_NET_PKT_WEIGHT);
>> }
>>
>> +static bool vhost_has_more_pkts(struct vhost_net *net,
>> + struct vhost_virtqueue *vq)
>> +{
>> + return !vhost_vq_avail_empty(&net->dev, vq) &&
>> + likely(!vhost_exceeds_maxpend(net));
> This really seems like mis-use of likely/unlikely, in the middle of a
> sequence of operations that will always be run when this function is
> called. I think you should remove the likely from this helper,
> especially, and control the branch from the branch point.

Yes, so I'm consider to make it a macro in next version.

>
>
>> +}
>> +
>> /* Expects to be always run from workqueue - which acts as
>> * read-size critical section for our kind of RCU. */
>> static void handle_tx(struct vhost_net *net)
>> @@ -578,8 +585,7 @@ static void handle_tx(struct vhost_net *net)
>> }
>> total_len += len;
>> if (total_len < VHOST_NET_WEIGHT &&
>> - !vhost_vq_avail_empty(&net->dev, vq) &&
>> - likely(!vhost_exceeds_maxpend(net))) {
>> + vhost_has_more_pkts(net, vq)) {
> Yes, I know it came from here, but likely/unlikely are for branch
> control, so they should encapsulate everything inside the if, unless
> I'm mistaken.

Ok.

>
>> msg.msg_flags |= MSG_MORE;
>> } else {
>> msg.msg_flags &= ~MSG_MORE;
>> @@ -605,7 +611,7 @@ static void handle_tx(struct vhost_net *net)
>> else
>> vhost_zerocopy_signal_used(net, vq);
>> vhost_net_tx_packet(net);
>> - if (unlikely(vhost_exceeds_weight(++sent_pkts, total_len))) {
>> + if (vhost_exceeds_weight(++sent_pkts, total_len)) {
> You should have kept the unlikely here, and not had it inside the
> helper (as per the previous patch. Also, why wasn't this change part
> of the previous patch?

Yes, will squash the above into previous one.

Thanks

>
>> vhost_poll_queue(&vq->poll);
>> break;
>> }