Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Mon, 27 May 2019 21:10:46 +0300
From:   Ivan Khoronzhuk <ivan.khoronzhuk@linaro.org>
To:     Jesper Dangaard Brouer <brouer@redhat.com>
Cc:     grygorii.strashko@ti.com, davem@davemloft.net, ast@kernel.org,
        linux-kernel@vger.kernel.org, linux-omap@vger.kernel.org,
        xdp-newbies@vger.kernel.org, ilias.apalodimas@linaro.org,
        netdev@vger.kernel.org, daniel@iogearbox.net,
        jakub.kicinski@netronome.com, john.fastabend@gmail.com,
        Tariq Toukan <tariqt@mellanox.com>
Subject: Re: [PATCH net-next 3/3] net: ethernet: ti: cpsw: add XDP support
Message-ID: <20190527181043.GA4246@khorivan>
Mail-Followup-To: Jesper Dangaard Brouer <brouer@redhat.com>,
        grygorii.strashko@ti.com, davem@davemloft.net, ast@kernel.org,
        linux-kernel@vger.kernel.org, linux-omap@vger.kernel.org,
        xdp-newbies@vger.kernel.org, ilias.apalodimas@linaro.org,
        netdev@vger.kernel.org, daniel@iogearbox.net,
        jakub.kicinski@netronome.com, john.fastabend@gmail.com,
        Tariq Toukan <tariqt@mellanox.com>
References: <20190523182035.9283-1-ivan.khoronzhuk@linaro.org>
 <20190523182035.9283-4-ivan.khoronzhuk@linaro.org>
 <20190524135418.5408591e@carbon>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii; format=flowed
Content-Disposition: inline
In-Reply-To: <20190524135418.5408591e@carbon>
User-Agent: Mutt/1.9.4 (2018-02-28)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Fri, May 24, 2019 at 01:54:18PM +0200, Jesper Dangaard Brouer wrote:
>On Thu, 23 May 2019 21:20:35 +0300
>Ivan Khoronzhuk <ivan.khoronzhuk@linaro.org> wrote:
>
>> Add XDP support based on rx page_pool allocator, one frame per page.
>> Page pool allocator is used with assumption that only one rx_handler
>> is running simultaneously. DMA map/unmap is reused from page pool
>> despite there is no need to map whole page.
>
>When using page_pool for DMA-mapping, your XDP-memory model must use
>1-page per packet, which you state you do.  This is because
>__page_pool_put_page() fallback mode does a __page_pool_clean_page()
>unmapping the DMA.  Ilias and I are looking at options for removing this
>restriction as Mlx5 would need it (when we extend the SKB to return
>pages to page_pool).
Thank for what you do, it can simplify a lot...

>
>Unfortunately, I've found another blocker for drivers using the DMA
>mapping feature of page_pool.  We don't properly handle the case, where
>a remote TX-driver have xdp_frame's in-flight, and simultaneously the
>sending driver is unloaded and take down the page_pool.  Nothing crash,
>but we end-up calling put_page() on a page that is still DMA-mapped.

Seems so, ... for generic solution, but looks like in case of cpsw there
is no issue due to "like direct" dma map by adding offset, so whether page_pool
dma map or dma map/unmap per rx/xmit, shouldn't be big difference.  Not sure
about all SoCs thought...

Despite of it, for cpsw I keep page_pool while down/up that I'm going to change
in v2.

>
>I'm working on different solutions for fixing this, see here:
> https://github.com/xdp-project/xdp-project/blob/master/areas/mem/page_pool03_shutdown_inflight.org
Hope there will be no changes in page_pool API.

>-- Best regards,
>  Jesper Dangaard Brouer
>  MSc.CS, Principal Kernel Engineer at Red Hat
>  LinkedIn: http://www.linkedin.com/in/brouer

-- 
Regards,
Ivan Khoronzhuk