On Mon, 21 Oct 2019 17:56:06 +0800, Zhu Yanjun wrote:
> On 2019/10/19 6:48, Jakub Kicinski wrote:
> > On Fri, 18 Oct 2019 06:01:25 -0400, Zhu Yanjun wrote:
> >> This change adds support for xmit_more based on the igb commit 6f19e12f6230
> >> ("igb: flush when in xmit_more mode and under descriptor pressure") and
> >> commit 6b16f9ee89b8 ("net: move skb->xmit_more hint to softnet data") that
> >> were made to igb to support this feature. The function netif_xmit_stopped
> >> is called to check if transmit queue on device is currently unable to send
> >> to determine if we must write the tail because we can add no further
> >> buffers.
> >> When normal packets and/or xmit_more packets fill up tx_desc, it is
> >> necessary to trigger NIC tx reg.
> > Looks broken. You gotta make sure you check the kick on _every_ return
> > path. There are 4 return statements in each function, you only touched
> > 2.
>
> In nv_start_xmit,
>
> [...]
>
> The above are dma_mapping_error. It seems that triggering NIC HW xmit is
> not needed.
>
> So when "tx_desc full" error, HW NIC xmit is triggerred. When
> dma_mapping_error,
>
> NIC HW xmit is not triggerred.
>
> That is why only 2 "return" are touched.
Imagine you have the following sequence of frames:
skbA | xmit_more() == true
skbB | xmit_more() == true
skbC | xmit_more() == true
skbD | xmit_more() == false
A, B, and C got queued successfully but the driver didn't kick the
queue because of xmit_more(). Now D gets dropped due to a DMA error.
Queue never gets kicked.
> > Also the labels should be lower case.
>
> This patch passes checkpatch.pl. It seems that "not lower case" is not a
> problem?
>
> If you think it is a problem, please show me where it is defined.
Look at this driver and at other kernel code. Labels are lower case,
upper case is for constants and macros.
