On Wed, Sep 7, 2016 at 7:58 PM, John Fastabend <john.fastab...@gmail.com> wrote: > On 16-09-07 11:22 AM, Jesper Dangaard Brouer wrote: >> >> On Wed, 7 Sep 2016 19:57:19 +0300 Saeed Mahameed <sae...@dev.mellanox.co.il> >> wrote: >>> On Wed, Sep 7, 2016 at 6:32 PM, Eric Dumazet <eric.duma...@gmail.com> wrote: >>>> On Wed, 2016-09-07 at 18:08 +0300, Saeed Mahameed wrote: >>>>> On Wed, Sep 7, 2016 at 5:41 PM, Eric Dumazet <eric.duma...@gmail.com> >>>>> wrote: >>>>>> On Wed, 2016-09-07 at 15:42 +0300, Saeed Mahameed wrote: >> [...] >>>> >>>> Only if a qdisc is present and pressure is high enough. >>>> >>>> But in a forwarding setup, we likely receive at a lower rate than the >>>> NIC can transmit. >> >> Yes, I can confirm this happens in my experiments. >> >>>> >>> >>> Jesper has a similar Idea to make the qdisc think it is under >>> pressure, when the device TX ring is idle most of the time, i think >>> his idea can come in handy here. I am not fully involved in the >>> details, maybe he can elaborate more. >>> >>> But if it works, it will be transparent to napi, and xmit more will >>> happen by design. >> >> Yes. I have some ideas around getting more bulking going from the qdisc >> layer, by having the drivers provide some feedback to the qdisc layer >> indicating xmit_more should be possible. This will be a topic at the >> Network Performance Workshop[1] at NetDev 1.2, I have will hopefully >> challenge people to come up with a good solution ;-) >> > > One thing I've noticed but haven't yet actually analyzed much is if > I shrink the nic descriptor ring size to only be slightly larger than > the qdisc layer bulking size I get more bulking and better perf numbers. > At least on microbenchmarks. The reason being the nic pushes back more > on the qdisc. So maybe a case for making the ring size in the NIC some > factor of the expected number of queues feeding the descriptor ring. >
BQL is not helping with that? Tom > .John
