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Date:   Thu, 4 Jul 2019 12:45:57 +0300
From:   Ivan Khoronzhuk <ivan.khoronzhuk@...aro.org>
To:     Jesper Dangaard Brouer <brouer@...hat.com>
Cc:     grygorii.strashko@...com, hawk@...nel.org, davem@...emloft.net,
        ast@...nel.org, linux-kernel@...r.kernel.org,
        linux-omap@...r.kernel.org, xdp-newbies@...r.kernel.org,
        ilias.apalodimas@...aro.org, netdev@...r.kernel.org,
        daniel@...earbox.net, jakub.kicinski@...ronome.com,
        john.fastabend@...il.com
Subject: Re: [PATCH v6 net-next 5/5] net: ethernet: ti: cpsw: add XDP support

On Thu, Jul 04, 2019 at 11:19:39AM +0200, Jesper Dangaard Brouer wrote:
>On Wed,  3 Jul 2019 13:19:03 +0300
>Ivan Khoronzhuk <ivan.khoronzhuk@...aro.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.
>>
>> Due to specific of cpsw, the same TX/RX handler can be used by 2
>> network devices, so special fields in buffer are added to identify
>> an interface the frame is destined to. Thus XDP works for both
>> interfaces, that allows to test xdp redirect between two interfaces
>> easily. Aslo, each rx queue have own page pools, but common for both
>> netdevs.
>>
>> XDP prog is common for all channels till appropriate changes are added
>> in XDP infrastructure. Also, once page_pool recycling becomes part of
>> skb netstack some simplifications can be added, like removing
>> page_pool_release_page() before skb receive.
>>
>> In order to keep rx_dev while redirect, that can be somehow used in
>> future, do flush in rx_handler, that allows to keep rx dev the same
>> while reidrect. It allows to conform with tracing rx_dev pointed
>> by Jesper.
>
>So, you simply call xdp_do_flush_map() after each xdp_do_redirect().
>It will kill RX-bulk and performance, but I guess it will work.
>
>I guess, we can optimized it later, by e.g. in function calling
>cpsw_run_xdp() have a variable that detect if net_device changed
>(priv->ndev) and then call xdp_do_flush_map() when needed.

It's problem of cpsw already and can be optimized locally by own
bulk queues for instance, if it will be simple if really needed ofc.

>
>
>> Signed-off-by: Ivan Khoronzhuk <ivan.khoronzhuk@...aro.org>
>> ---
>>  drivers/net/ethernet/ti/Kconfig        |   1 +
>>  drivers/net/ethernet/ti/cpsw.c         | 485 ++++++++++++++++++++++---
>>  drivers/net/ethernet/ti/cpsw_ethtool.c |  66 +++-
>>  drivers/net/ethernet/ti/cpsw_priv.h    |   7 +
>>  4 files changed, 502 insertions(+), 57 deletions(-)
>>
>[...]
>> +static int cpsw_run_xdp(struct cpsw_priv *priv, int ch, struct xdp_buff *xdp,
>> +			struct page *page)
>> +{
>> +	struct cpsw_common *cpsw = priv->cpsw;
>> +	struct net_device *ndev = priv->ndev;
>> +	int ret = CPSW_XDP_CONSUMED;
>> +	struct xdp_frame *xdpf;
>> +	struct bpf_prog *prog;
>> +	u32 act;
>> +
>> +	rcu_read_lock();
>> +
>> +	prog = READ_ONCE(priv->xdp_prog);
>> +	if (!prog) {
>> +		ret = CPSW_XDP_PASS;
>> +		goto out;
>> +	}
>> +
>> +	act = bpf_prog_run_xdp(prog, xdp);
>> +	switch (act) {
>> +	case XDP_PASS:
>> +		ret = CPSW_XDP_PASS;
>> +		break;
>> +	case XDP_TX:
>> +		xdpf = convert_to_xdp_frame(xdp);
>> +		if (unlikely(!xdpf))
>> +			goto drop;
>> +
>> +		cpsw_xdp_tx_frame(priv, xdpf, page);
>> +		break;
>> +	case XDP_REDIRECT:
>> +		if (xdp_do_redirect(ndev, xdp, prog))
>> +			goto drop;
>> +
>> +		/* as flush requires rx_dev to be per NAPI handle and there
>> +		 * is can be two devices putting packets on bulk queue,
>> +		 * do flush here avoid this just for sure.
>> +		 */
>> +		xdp_do_flush_map();
>
>> +		break;
>> +	default:
>> +		bpf_warn_invalid_xdp_action(act);
>> +		/* fall through */
>> +	case XDP_ABORTED:
>> +		trace_xdp_exception(ndev, prog, act);
>> +		/* fall through -- handle aborts by dropping packet */
>> +	case XDP_DROP:
>> +		goto drop;
>> +	}
>> +out:
>> +	rcu_read_unlock();
>> +	return ret;
>> +drop:
>> +	rcu_read_unlock();
>> +	page_pool_recycle_direct(cpsw->page_pool[ch], page);
>> +	return ret;
>> +}
>
>-- 
>Best regards,
>  Jesper Dangaard Brouer
>  MSc.CS, Principal Kernel Engineer at Red Hat
>  LinkedIn: http://www.linkedin.com/in/brouer

-- 
Regards,
Ivan Khoronzhuk

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