On 2016年11月11日 12:17, John Fastabend wrote:
On 16-11-10 07:31 PM, Michael S. Tsirkin wrote:
>On Fri, Nov 11, 2016 at 10:07:44AM +0800, Jason Wang wrote:
>>
>>
>>On 2016年11月10日 00:38, Michael S. Tsirkin wrote:
>>>On Wed, Nov 09, 2016 at 03:38:31PM +0800, Jason Wang wrote:
>>>>Backlog were used for tuntap rx, but it can only process 1 packet at
>>>>one time since it was scheduled during sendmsg() synchronously in
>>>>process context. This lead bad cache utilization so this patch tries
>>>>to do some batching before call rx NAPI. This is done through:
>>>>
>>>>- accept MSG_MORE as a hint from sendmsg() caller, if it was set,
>>>> batch the packet temporarily in a linked list and submit them all
>>>> once MSG_MORE were cleared.
>>>>- implement a tuntap specific NAPI handler for processing this kind of
>>>> possible batching. (This could be done by extending backlog to
>>>> support skb like, but using a tun specific one looks cleaner and
>>>> easier for future extension).
>>>>
>>>>Signed-off-by: Jason Wang<jasow...@redhat.com>
>>>So why do we need an extra queue?
>>
>>The idea was borrowed from backlog to allow some kind of bulking and avoid
>>spinlock on each dequeuing.
>>
>>> This is not what hardware devices do.
>>>How about adding the packet to queue unconditionally, deferring
>>>signalling until we get sendmsg without MSG_MORE?
>>
>>Then you need touch spinlock when dequeuing each packet.
>
Random thought, I have a cmpxchg ring I am using for the qdisc work that
could possibly replace the spinlock implementation. I haven't figured
out the resizing API yet because I did not need it but I assume it could
help here and let you dequeue multiple skbs in one operation.
I can post the latest version if useful or an older version is
somewhere on patchworks as well.
.John
Look useful here, and I can compare the performance if you post.
A question is can we extend the skb_array to support that?
Thanks
