linux-kernel - Re: [PATCH net] net: fec: tx processing does not call XDP APIs if budget is 0

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Message-ID: <20230726211450.209efe35@kernel.org>
Date:   Wed, 26 Jul 2023 21:14:50 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Wei Fang <wei.fang@....com>
Cc:     Alexander Duyck <alexander.duyck@...il.com>,
        dl-linux-imx <linux-imx@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        Shenwei Wang <shenwei.wang@....com>,
        Clark Wang <xiaoning.wang@....com>,
        "pabeni@...hat.com" <pabeni@...hat.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH net] net: fec: tx processing does not call XDP APIs if
 budget is 0

On Thu, 27 Jul 2023 02:08:32 +0000 Wei Fang wrote:
> > Actually after talking with Jakub a bit more there is an issue here,
> > but not freeing the frames isn't the solution. We likely need to just
> > fix the page pool code so that it doesn't attempt to recycle the
> > frames if operating in IRQ context.
> > 
> > The way this is dealt with for skbs is that we queue skbs if we are in
> > IRQ context so that it can be deferred to be freed by the
> > net_tx_action. We likely need to look at doing something similar for
> > page_pool pages or XDP frames.
> >   
> After reading your discussion with Jakub, I understand this issue a bit more.
> But we are not sure when this issue will be fixed in page pool, currently we
> can only tolerate a delay in sending of a netpoll message. So I think this patch
> is necessary, and I will refine it in the future when the page pool has fixed the
> issue. In addition, as you mentioned before, napi_consume_skb should be
> used to instead of dev_kfree_skb_any, so I will improve this patch in version 2.

I think so too, since the patch can only help, you already wrote it and
it won't be extra backporting work since the code is only present in
6.5 - I think it's worth applying. And we can refine things as page pool
limitations get listed (the napi_consume_skb() is net-next material,
anyway).