linux-kernel - RE: [PATCH v2 net 2/9] net: enetc: correct the tx

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Message-ID:
 <PAXPR04MB8510ECBBA69BD5E50DB1C03088C72@PAXPR04MB8510.eurprd04.prod.outlook.com>
Date: Fri, 21 Feb 2025 08:34:22 +0000
From: Wei Fang <wei.fang@....com>
To: Claudiu Manoil <claudiu.manoil@....com>, Vladimir Oltean
	<vladimir.oltean@....com>
CC: 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>, Ioana Ciornei
	<ioana.ciornei@....com>, "Y.B. Lu" <yangbo.lu@....com>,
	"michal.swiatkowski@...ux.intel.com" <michal.swiatkowski@...ux.intel.com>,
	"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>, "stable@...r.kernel.org"
	<stable@...r.kernel.org>
Subject: RE: [PATCH v2 net 2/9] net: enetc: correct the tx_swbd statistics

> > > I'm not sure "correct the statistics" is the best way to describe this
> > > change. Maybe "keep track of correct TXBD count in
> > > enetc_map_tx_tso_buffs()"?
> >
> > Hi Vladimir,
> >
> > Inspired by Michal, I think we don't need to keep the count variable, because
> > we already have index "i", we just need to record the value of the initial i at
> the
> > beginning. So I plan to do this optimization on the net-next tree in the future.
> > So I don't think it is necessary to modify enetc_map_tx_tso_hdr().
> >
> 
> And what if 'i' wraps around at least one time and becomes greater than the
> initial 'i'? Instead of 'count' you would have to record the number of wraps.

I think this situation will not happen, because when calling
enetc_map_tx_tso_buffs()/enetc_map_tx_buffs()/enetc_lso_hw_offload(),
we always check whether the current free BDs are enough. The number of
free BDs is always <= bdr->bd_count, in the case you mentioned, the frame
will occupy more BDs than bdr->bd_count.

> Even if not possible now in specific cases, there should be no limitation on
> whether 'i' can wrap around in the loop or not (i.e. maybe some users want to
> try very small Tx rings etc.)