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From:   "Pandey, Radhey Shyam" <radhey.shyam.pandey@amd.com>
To:     Jakub Kicinski <kuba@kernel.org>
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Subject: RE: [PATCH net-next v7 3/3] net: axienet: Introduce dmaengine support
Thread-Topic: [PATCH net-next v7 3/3] net: axienet: Introduce dmaengine
 support
Thread-Index: AQHZ8XmjDysNxqIG3UGZtitzZHc+JbA6JqaAgAL7GNCAADSGAIAEbQqw
Date:   Mon, 9 Oct 2023 19:41:35 +0000
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> -----Original Message-----
> From: Jakub Kicinski <kuba@kernel.org>
> Sent: Saturday, October 7, 2023 3:03 AM
> To: Pandey, Radhey Shyam <radhey.shyam.pandey@amd.com>
> Cc: davem@davemloft.net; edumazet@google.com; pabeni@redhat.com;
> robh+dt@kernel.org; krzysztof.kozlowski+dt@linaro.org;
> conor+dt@kernel.org; Simek, Michal <michal.simek@amd.com>;
> linux@armlinux.org.uk; f.fainelli@gmail.com; netdev@vger.kernel.org;
> devicetree@vger.kernel.org; linux-kernel@vger.kernel.org; linux-arm-
> kernel@lists.infradead.org; git (AMD-Xilinx) <git@amd.com>
> Subject: Re: [PATCH net-next v7 3/3] net: axienet: Introduce dmaengine
> support
>=20
> On Fri, 6 Oct 2023 19:04:29 +0000 Pandey, Radhey Shyam wrote:
> > > > +		netif_stop_queue(ndev);
> > > > +		if (net_ratelimit())
> > > > +			netdev_warn(ndev, "TX ring unexpectedly full\n");
> > >
> > > I don't see you stopping the queue when the ring gets full, am I not
> > > looking into the right place? Otherwise this is sort of expected to
> > > occasionally hapen
> >
> > We are calling stop_queue if TX ring is full. Is that what you meant?
> > netif_stop_queue(ndev);
>=20
> But somewhere else or just here after printing the warning?

There is call to netif_stop_queue(ndev) just before this netdev_warn.
I copied below for quick reference.

+	sg_len =3D skb_shinfo(skb)->nr_frags + 1;
+	if (!CIRC_SPACE(lp->tx_ring_head, lp->tx_ring_tail, TX_BD_NUM_MAX)) {
+		netif_stop_queue(ndev);
+		if (net_ratelimit())
+			netdev_warn(ndev, "TX ring unexpectedly full\n");
+		return NETDEV_TX_BUSY;
+	}

However, I noticed above check doesn't account for all frags - so will=20
modify the if check to see if available space is less than sg_len. If yes, =
then=20
stop the queue and return busy , else continue with xmit.

>=20
> The recommended flow is to stop the queue after enqueuing a packet
> successfully, if the remaining space is not enough to hold an skb with al=
l frags
> populated. That avoids ever returning BUSY.