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Date:   Thu, 4 Jul 2019 16:06:35 +0300
From:   Ilias Apalodimas <ilias.apalodimas@linaro.org>
To:     Jose Abreu <Jose.Abreu@synopsys.com>
Cc:     Jesper Dangaard Brouer <brouer@redhat.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
        "linux-stm32@st-md-mailman.stormreply.com" 
        <linux-stm32@st-md-mailman.stormreply.com>,
        "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>,
        Joao Pinto <Joao.Pinto@synopsys.com>,
        "David S . Miller" <davem@davemloft.net>,
        Giuseppe Cavallaro <peppe.cavallaro@st.com>,
        Alexandre Torgue <alexandre.torgue@st.com>,
        Maxime Coquelin <mcoquelin.stm32@gmail.com>,
        Maxime Ripard <maxime.ripard@bootlin.com>,
        Chen-Yu Tsai <wens@csie.org>
Subject: Re: [PATCH net-next 3/3] net: stmmac: Introducing support for Page
 Pool
Message-ID: <20190704130635.GA10412@apalos>
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Hi Jose, 

> Thank you all for your review comments !
> 
> From: Ilias Apalodimas <ilias.apalodimas@linaro.org>
> 
> > 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