From: Jeff Kirsher
> Sent: 06 October 2017 18:57
> From: Jacob Keller <jacob.e.kel...@intel.com>
>
> Since commit 6a7fded776a7 ("i40e: Fix RS bit update in Tx path and
> disable force WB workaround") we've tried to "optimize" setting the
> RS bit based around skb->xmit_more. This same logic was refactored
> in commit 1dc8b538795f ("i40e: Reorder logic for coalescing RS bits"),
> but ultimately was not functionally changed.
I've tried to understand the above, but without definitions of WB
and RS and the '4-ness' of something it is quite difficult.
I THINK this is all about telling the hardware there is a packet
in the ring to transmit?
I don't understand the 4-ness. Linux requires that the hardware
be notified of a single packet transmit, and that the 'transmit
complete' also be notified in 'a timely manner' for a single packet.
skb->xmit_more ought to be usable to optimise both of these
(assuming it isn't a lie).
The driver would need to ensure a ring full of messages isn't
generated without either wakeup - but that might be 128 frames.
FWIW on the systems I have PCIe writes are relatively cheap
(reads are slow). So different counts would be appropriate
for delaying doorbell writes and requesting completion interrupts.
David
