Re: [PATCH net v2] r8152: avoid the driver drops a lot of packets

On Thu, 7 Sep 2023 07:16:50 +0000 Hayes Wang wrote:

quoted

Before we tweak the heuristics let's make sure rx_bottom() behaves
correctly. Could you make sure that
 - we don't perform _any_ rx processing when budget is 0
   (see the NAPI documentation under Documentation/networking)  

The work_done would be 0, and napi_complete_done() wouldn't be called.
However, skb_queue_len(&tp->rx_queue) may be increased. I think it is
not acceptable, right?

If budget is 0 we got called by netconsole, meaning we may be holding
arbitrary locks. And we can't use napi_alloc_skb() which is for
softirq/bh context only. We should only try to complete Tx in that
case, since r8152_poll() doesn't handle any Tx the right thing seems
to be to add if (!budget) return 0;

quoted

 - finish the current aggregate even if budget run out, return
   work_done = budget in that case.
   With this change the rx_queue thing should be gone completely.  

Excuse me. I don't understand this part. I know that when the packets are
more than budget, the maximum packets which could be handled is budget.
That is, return work_done = budget. However, the extra packets would be queued
to rx_queue. I don't understand what you mean about " the rx_queue thing
should be gone completely". I think the current driver would return
work_done = budget, and queue the other packets. I don't sure what you
want me to change.

Nothing will explode if we process a few more packets than budget
(assuming budget > 0). If we already do allocations and prepare
those skbs - there's no point holding onto them in the driver.
Just sent them up the stack (and then we won't need the local rx_queue).

quoted

 - instead of copying the head use napi_get_frags() + napi_gro_frags()
   it gives you an skb, you just attach the page to it as a frag and
   hand it back to GRO. This makes sure you never pull data into head
   rather than just headers.  

I would study about them. Thanks.

Should I include above changes for this patch?
I think I have to submit another patches for above.

quoted

Please share the performance results with those changes.  

I couldn't reproduce the problem, so I couldn't provide the result
with the differences.

Hm, if you can't repro my intuition would be to only take the patch for
budget=0 handling into net, and the rest as improvements into net-next.