Subject: Re: [PATCH net-next 3/3] net: stmmac: Introducing support for Page Pool

From: Ilias Apalodimas <[email-masked]>
Date: Thu, 4 Jul 2019 16:06:35 +0300

Hi Jose, 

> Thank you all for your review comments !
> 
> From: Ilias Apalodimas <[email-masked]>
> 
> > That's why i was concerned on what will happen on > 1000b frames and what the
> > memory pressure is going to be. 
> > The trade off here is copying vs mapping/unmapping.
> 
> Well, the performance numbers I mentioned are for TSO with default MTU 
> (1500) and using iperf3 with zero-copy. Here follows netperf:
> 

Ok i guess this should be fine. Here's why.
You'll allocate an extra memory from page pool API which equals
the number of descriptors * 1 page.
You also allocate SKB's to copy the data and recycle the page pool buffers.
So page_pool won't add any significant memory pressure since we expect *all*
it's buffers to be recycled. 
The SKBs are allocated anyway in the current driver so bottom line you trade off
some memory (the page_pool buffers) + a memcpy per packet and skip the dma
map/unmap which is the bottleneck in your hardware. 
I think it's fine

Cheers
/Ilias