Hi everyone, > -----Original Message----- > From: dev [mailto:dev-boun...@dpdk.org] On Behalf Of Ferruh Yigit > Sent: Friday, March 9, 2018 3:04 PM > To: John Daley <johnd...@cisco.com> > Cc: dev@dpdk.org; Hyong Youb Kim <hyon...@cisco.com> > Subject: Re: [dpdk-dev] [PATCH v3 03/10] net/enic: heed the requested max Rx > packet size > > On 3/8/2018 2:46 AM, John Daley wrote: > > From: Hyong Youb Kim <hyon...@cisco.com> > > > > Currently, enic completely ignores the requested max Rx packet size > > (rxmode.max_rx_pkt_len). The desired behavior is that the NIC hardware > > drops packets larger than the requested size, even though they are > > still smaller than MTU. > > Your description looks reasonable but is there reason of two levels of limits, > max_rx_pkt_len and MTU, why not just use MTU. There is already a mail thread > to > clarify max_rx_pkt_len [1]. > > Is this work based on an application that uses max_rx_pkt_len and to make PMD > compatible with that application? If so we can continue with patch, but if the > patch is to implement DPDK properly I suggest postponing this until > max_rx_pkt_len clarified. > > [1] > https://dpdk.org/ml/archives/dev/2018-March/092178.html
I think there are quite a lot apps these days that might rely on setting MTU via rxmode.max_rx_pkt_len. I think we need to support them till we (ever) deprecate rxmode.max_rx_pkt_len. Konstantin > > > > > Cisco VIC does not have such a feature. But, we can accomplish a > > similar (not same) effect by reducing the size of posted receive > > buffers. Packets larger than the posted size get truncated, and the > > receive handler drops them. This is also how the kernel enic driver > > enforces the Rx side MTU. > > > > This workaround works only when scatter mode is *not* used. When > > scatter is used, there is currently no way to support > > rxmode.max_rx_pkt_len, as the NIC always receives packets up to MTU. > > > > For posterity, add a copious amount of comments regarding the > > hardware's drop/receive behavior with respect to max/current MTU. > > > > Signed-off-by: Hyong Youb Kim <hyon...@cisco.com> > > Reviewed-by: John Daley <johnd...@cisco.com> > > <...>
