netdev - Re: [PATCH net-next] macvtap/macvlan: use IFF_NO

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Date:	Tue, 25 Aug 2015 12:32:35 -0400
From:	Vlad Yasevich <vyasevic@...hat.com>
To:	Jason Wang <jasowang@...hat.com>,
	"Michael S. Tsirkin" <mst@...hat.com>
CC:	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	Patrick McHardy <kaber@...sh.net>
Subject: Re: [PATCH net-next] macvtap/macvlan: use IFF_NO_QUEUE

On 08/25/2015 07:30 AM, Jason Wang wrote:
> 
> 
> On 08/25/2015 06:17 PM, Michael S. Tsirkin wrote:
>> On Mon, Aug 24, 2015 at 04:33:12PM +0800, Jason Wang wrote:
>>>> 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 <kaber@...sh.net>
>>>> Cc: Vladislav Yasevich <vyasevic@...hat.com>
>>>> Cc: Michael S. Tsirkin <mst@...hat.com>
>>>> Signed-off-by: Jason Wang <jasowang@...hat.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
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