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Date:   Thu, 29 Sep 2022 17:39:56 +0200
From:   Andrew Lunn <andrew@lunn.ch>
To:     Jesper Dangaard Brouer <jbrouer@redhat.com>
Cc:     Shenwei Wang <shenwei.wang@nxp.com>, brouer@redhat.com,
        Joakim Zhang <qiangqing.zhang@nxp.com>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Jesper Dangaard Brouer <hawk@kernel.org>,
        John Fastabend <john.fastabend@gmail.com>,
        "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "imx@lists.linux.dev" <imx@lists.linux.dev>
Subject: Re: [EXT] Re: [PATCH 1/1] net: fec: add initial XDP support
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On Thu, Sep 29, 2022 at 05:28:43PM +0200, Jesper Dangaard Brouer wrote:
> 
> 
> On 29/09/2022 15.26, Shenwei Wang wrote:
> > 
> > > From: Andrew Lunn <andrew@lunn.ch>
> > > Sent: Thursday, September 29, 2022 8:23 AM
> [...]
> > > 
> > > > I actually did some compare testing regarding the page pool for normal
> > > > traffic.  So far I don't see significant improvement in the current
> > > > implementation. The performance for large packets improves a little,
> > > > and the performance for small packets get a little worse.
> > > 
> > > What hardware was this for? imx51? imx6? imx7 Vybrid? These all use the FEC.
> > 
> > I tested on imx8qxp platform. It is ARM64.
> 
> On mvneta driver/platform we saw huge speedup replacing:
> 
>   page_pool_release_page(rxq->page_pool, page);
> with
>   skb_mark_for_recycle(skb);
> 
> As I mentioned: Today page_pool have SKB recycle support (you might have
> looked at drivers that didn't utilize this yet), thus you don't need to
> release the page (page_pool_release_page) here.  Instead you could simply
> mark the SKB for recycling, unless driver does some page refcnt tricks I
> didn't notice.
> 
> On the mvneta driver/platform the DMA unmap (in page_pool_release_page) was
> very expensive. This imx8qxp platform might have faster DMA unmap in case is
> it cache-coherent.

I don't know about imx8qxp, but i've played with imx6 and Vybrid, and
cache flush and invalidate are very expensive.

      Andrew