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From:   Shenwei Wang <shenwei.wang@nxp.com>
To:     Andrew Lunn <andrew@lunn.ch>
CC:     Joakim Zhang <qiangqing.zhang@nxp.com>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
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        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
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        John Fastabend <john.fastabend@gmail.com>,
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        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "imx@lists.linux.dev" <imx@lists.linux.dev>
Subject: RE: [EXT] Re: [PATCH 1/1] net: fec: add initial XDP support
Thread-Topic: [EXT] Re: [PATCH 1/1] net: fec: add initial XDP support
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Date:   Thu, 29 Sep 2022 13:35:05 +0000
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> -----Original Message-----
> From: Andrew Lunn <andrew@lunn.ch>
> Sent: Thursday, September 29, 2022 8:24 AM
> To: Shenwei Wang <shenwei.wang@nxp.com>
> Cc: Joakim Zhang <qiangqing.zhang@nxp.com>; David S. Miller
> <davem@davemloft.net>; Eric Dumazet <edumazet@google.com>; Jakub
> Kicinski <kuba@kernel.org>; Paolo Abeni <pabeni@redhat.com>; Alexei
> Starovoitov <ast@kernel.org>; Daniel Borkmann <daniel@iogearbox.net>;
> Jesper Dangaard Brouer <hawk@kernel.org>; John Fastabend
> <john.fastabend@gmail.com>; netdev@vger.kernel.org; linux-
> kernel@vger.kernel.org; imx@lists.linux.dev
> Subject: Re: [EXT] Re: [PATCH 1/1] net: fec: add initial XDP support
>=20
> Caution: EXT Email
>=20
> > > > +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.
> > >
> >
>=20
> > As this increment is only executed under the NAPI kthread context, is
> > the protection still required?
>=20
> Are the statistics values read by ethtool under NAPI kthread context?
>=20

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

Thanks,
Shenwei

>     Andrew