lkml.org 
[lkml]   [2022]   [Mar]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH net-next v2 9/9] net: ethernet: mtk-star-emac: separate tx/rx handling with two NAPIs
From
Date
Dear Jakub,
Thanks for your comments~

On Mon, 2022-03-14 at 08:57 -0700, Jakub Kicinski wrote:
> On Mon, 14 Mar 2022 15:01:23 +0800 Biao Huang wrote:
> > > Drivers are expected to stop their queues at the end of xmit
> > > routine
> > > if
> > > the ring can't accommodate another frame. It's more efficient to
> > > stop
> > > the queues early than have to put skbs already dequeued from the
> > > qdisc
> > > layer back into the qdiscs.
> >
> > Yes, if descriptors ring is full, it's meaningful to stop the
> > queue
> > at the end of xmit;
> > But driver seems hard to know how many descriptors the next skb
> > will
> > request, e.g. 3 descriptors are available for next round send, but
> > the
> > next skb may need 4 descriptors, in this case, we still need judge
> > whether descriptors are enough for skb transmission, then decide
> > stop
> > the queue or not, at the beginning of xmit routine.
> >
> > Maybe we should judge ring is full or not at the beginning and the
> > end
> > of xmit routine(seems a little redundancy).
>
> Assume the worst case scenario. You set the default ring size to 512,
> skb can have at most MAX_SKB_FRAGS fragments (usually 17) so the max
> number of descriptors should not be very high, hard to pre-compute,
> or problematic compared to the total ring size.
Yes, we'll check the available descriptor number at the end of xmit
routine, and ensure it will larger than (MAX_SKB_FRAGS + 1) in next
send. (refer to stmmac_main.c)

Regards!

\
 
 \ /
  Last update: 2022-03-15 02:00    [W:0.074 / U:0.320 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site