On 08/26/2015 12:32 AM, Vlad Yasevich wrote:

On 08/25/2015 07:30 AM, Jason Wang wrote:

quoted

On 08/25/2015 06:17 PM, Michael S. Tsirkin wrote:

quoted

On Mon, Aug 24, 2015 at 04:33:12PM +0800, Jason Wang wrote:

quoted

quoted

For macvlan, switch to use IFF_NO_QUEUE instead of tx_queue_len = 0.

For macvtap, after commit 6acf54f1cf0a6747bac9fea26f34cfc5a9029523
("macvtap: Add support of packet capture on macvtap
device."). Multiqueue macvtap suffers from single qdisc lock
contention. This is because macvtap claims a non zero tx_queue_len and
it reuses this value as it socket receive queue size.Thanks to
IFF_NO_QUEUE, we can remove the lock contention without breaking
existing socket receive queue length logic.

Cc: Patrick McHardy <redacted>
Cc: Vladislav Yasevich <redacted>
Cc: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>

Seems to make sense. Give me a day or two to get over the jet lag
(and get out from under the pile of mail accumulated while I was traveling),
I'll review properly and ack.

A note on this patch: only default qdisc were removed but we don't lose
the ability to attach a qdisc to macvtap (though it may cause lock
contention on multiqueue case).

Wouldn't that lock contention be solved if we really had multiple queues
for multi-queue macvtaps?

-vlad

Yes, but this introduce another layer of txq locks contention? And it
also needs macvlan multiqueue support. We used to do something like this
but switch to NETIF_F_LLTX finally. You may refer:

2c11455321f37da6fe6cc36353149f9ac9183334 macvlan: add multiqueue capability
8ffab51b3dfc54876f145f15b351c41f3f703195 macvlan: lockless tx path