netdev - RE: [PATCH v2 net-next 2/5] net: enetc: add Tx checksum offload for i.MX95 ENETC

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Message-ID:
 <PAXPR04MB8510E069CF5426543813A62888592@PAXPR04MB8510.eurprd04.prod.outlook.com>
Date: Tue, 12 Nov 2024 01:24:03 +0000
From: Wei Fang <wei.fang@....com>
To: Claudiu Manoil <claudiu.manoil@....com>
CC: "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"imx@...ts.linux.dev" <imx@...ts.linux.dev>, Vladimir Oltean
	<vladimir.oltean@....com>, Clark Wang <xiaoning.wang@....com>,
	"andrew+netdev@...n.ch" <andrew+netdev@...n.ch>, "davem@...emloft.net"
	<davem@...emloft.net>, "edumazet@...gle.com" <edumazet@...gle.com>,
	"kuba@...nel.org" <kuba@...nel.org>, "pabeni@...hat.com" <pabeni@...hat.com>,
	Frank Li <frank.li@....com>
Subject: RE: [PATCH v2 net-next 2/5] net: enetc: add Tx checksum offload for
 i.MX95 ENETC

> > > -----Original Message-----
> > > From: Wei Fang
> > > Sent: 2024年11月11日 17:26
> > > To: Claudiu Manoil <claudiu.manoil@....com>
> > > Cc: netdev@...r.kernel.org; linux-kernel@...r.kernel.org;
> > > imx@...ts.linux.dev; Vladimir Oltean <vladimir.oltean@....com>; Clark
> > > Wang <xiaoning.wang@....com>; andrew+netdev@...n.ch;
> > > davem@...emloft.net; edumazet@...gle.com; kuba@...nel.org;
> > > pabeni@...hat.com; Frank Li <frank.li@....com>
> > > Subject: RE: [PATCH v2 net-next 2/5] net: enetc: add Tx checksum
> > > offload for
> > > i.MX95 ENETC
> > >
> > > > > --- a/drivers/net/ethernet/freescale/enetc/enetc.c
> > > > > +++ b/drivers/net/ethernet/freescale/enetc/enetc.c
> > > > > @@ -143,6 +143,27 @@ static int enetc_ptp_parse(struct sk_buff
> > > > > *skb, u8 *udp,
> > > > >  	return 0;
> > > > >  }
> > > > >
> > > > > +static bool enetc_tx_csum_offload_check(struct sk_buff *skb) {
> > > > > +	if (ip_hdr(skb)->version == 4)
> > > >
> > > > I would avoid using ip_hdr(), or any form of touching packed data
> > > > and try extract this kind of info directly from the skb metadata
> > > > instead, see also comment below.
> > > >
> > > > i.e., why not:
> > > > if (skb->protocol == htons(ETH_P_IPV6)) ..  etc. ?
> > >
> > > skb->protocol may be VLAN protocol, such as ETH_P_8021Q,
> > ETH_P_8021AD.
> > > If so, it is impossible to determine whether it is an IPv4 or IPv6
> > > frames through protocol.
> > >
> > > > or
> > > > switch (skb->csum_offset) {
> > > > case offsetof(struct tcphdr, check):
> > > > [...]
> > > > case offsetof(struct udphdr, check):
> > > > [...]
> > >
> > > This seems to be able to be used to determine whether it is a UDP or
> > > TCP frame.
> > > Thanks.
> > >
> > > >
> > > > > +		return ip_hdr(skb)->protocol == IPPROTO_TCP ||
> > > > > +		       ip_hdr(skb)->protocol == IPPROTO_UDP;
> > > > > +
> > > > > +	if (ip_hdr(skb)->version == 6)
> > > > > +		return ipv6_hdr(skb)->nexthdr == NEXTHDR_TCP ||
> > > > > +		       ipv6_hdr(skb)->nexthdr == NEXTHDR_UDP;
> > > > > +
> > > > > +	return false;
> > > > > +}
> > > > > +
> > > > > +static bool enetc_skb_is_tcp(struct sk_buff *skb) {
> > > >
> > > > There is a more efficient way of checking if L4 is TCP, without
> > > > touching packet data, i.e. through the 'csum_offset' skb field:
> > > > return skb->csum_offset == offsetof(struct tcphdr, check);
> > > >
> > > > Pls. have a look at these optimizations, I would expect visible
> > > > improvements in throughput. Thanks.
> > >
> > > For small packets this might improve performance, but I'm not sure if
> > > it would be a significant improvement. :)
> > >
> >
> > I didn't see any visible improvements in performance after using csum_offset.
> > For example, when using pktgen to send 10,000,000 packets, the time taken
> is
> > almost the same regardless of whether they are large or small packets, and
> the
> > CPU idle ratio seen through the top command is also basically the same.
> Also,
> > the UDP performance tested by iperf3 is basically the same.
> >
> 
> Maybe there's a bigger bottleneck somewhere else. I would change
> enetc_skb_is_tcp()
> regardless, instead of 'if (ip_hdr() == 4) ... else ...', you can have the one line
> return statement
> above.
> 

Yeah, I can refine enetc_skb_is_tcp() and enetc_tx_csum_offload_check()
through csum_offset, this is logically simpler.

> As commented before, I would try to get rid of any access to packet content if
> skb metadata
> fields could be used instead, but I don have a solution now on how to retrieve
> the IP protocol
> version this way.
> 
> Thanks for testing anyway.
>