linux-kernel - RE: [EXT] Re: [PATCH 1/1] net: fec: add initial XDP support

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Message-ID: <PAXPR04MB9185B9A02BBC7A861C6B75BA89579@PAXPR04MB9185.eurprd04.prod.outlook.com>
Date:   Thu, 29 Sep 2022 13:35:05 +0000
From:   Shenwei Wang <shenwei.wang@....com>
To:     Andrew Lunn <andrew@...n.ch>
CC:     Joakim Zhang <qiangqing.zhang@....com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.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>
Subject: RE: [EXT] Re: [PATCH 1/1] net: fec: add initial XDP support



> -----Original Message-----
> From: Andrew Lunn <andrew@...n.ch>
> Sent: Thursday, September 29, 2022 8:24 AM
> To: Shenwei Wang <shenwei.wang@....com>
> Cc: Joakim Zhang <qiangqing.zhang@....com>; David S. Miller
> <davem@...emloft.net>; Eric Dumazet <edumazet@...gle.com>; Jakub
> Kicinski <kuba@...nel.org>; Paolo Abeni <pabeni@...hat.com>; Alexei
> Starovoitov <ast@...nel.org>; Daniel Borkmann <daniel@...earbox.net>;
> Jesper Dangaard Brouer <hawk@...nel.org>; John Fastabend
> <john.fastabend@...il.com>; netdev@...r.kernel.org; linux-
> kernel@...r.kernel.org; imx@...ts.linux.dev
> Subject: Re: [EXT] Re: [PATCH 1/1] net: fec: add initial XDP support
> 
> Caution: EXT Email
> 
> > > > +struct fec_enet_xdp_stats {
> > > > +     u64     xdp_pass;
> > > > +     u64     xdp_drop;
> > > > +     u64     xdp_xmit;
> > > > +     u64     xdp_redirect;
> > > > +     u64     xdp_xmit_err;
> > > > +     u64     xdp_tx;
> > > > +     u64     xdp_tx_err;
> > > > +};
> > > > +
> > > > +     switch (act) {
> > > > +     case XDP_PASS:
> > > > +             rxq->stats.xdp_pass++;
> > >
> > > Since the stats are u64, and most machines using the FEC are 32 bit,
> > > you cannot just do an increment. Took a look at u64_stats_sync.h.
> > >
> >
> 
> > As this increment is only executed under the NAPI kthread context, is
> > the protection still required?
> 
> Are the statistics values read by ethtool under NAPI kthread context?
> 

You are right. The read is not under NAPI context.

Thanks,
Shenwei

>     Andrew