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From:   Shenwei Wang <shenwei.wang@nxp.com>
To:     Andrew Lunn <andrew@lunn.ch>,
        Alexander Lobakin <alexandr.lobakin@intel.com>
CC:     "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>,
        Jesper Dangaard Brouer <hawk@kernel.org>,
        John Fastabend <john.fastabend@gmail.com>,
        Wei Fang <wei.fang@nxp.com>,
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        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "imx@lists.linux.dev" <imx@lists.linux.dev>,
        kernel test robot <lkp@intel.com>
Subject: RE: [EXT] Re: [PATCH v3 1/1] net: fec: add xdp and page pool
 statistics
Thread-Topic: [EXT] Re: [PATCH v3 1/1] net: fec: add xdp and page pool
 statistics
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Date:   Mon, 14 Nov 2022 15:06:04 +0000
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References: <20221111153505.434398-1-shenwei.wang@nxp.com>
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 <Y3JLz1niXbdVbRH9@lunn.ch>
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> -----Original Message-----
> From: Andrew Lunn <andrew@lunn.ch>
> Sent: Monday, November 14, 2022 8:08 AM
> To: Alexander Lobakin <alexandr.lobakin@intel.com>
> Cc: Shenwei Wang <shenwei.wang@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>; Wei Fang <wei.fang@nxp.com>;
> netdev@vger.kernel.org; linux-kernel@vger.kernel.org; imx@lists.linux.dev=
;
> kernel test robot <lkp@intel.com>
> Subject: [EXT] Re: [PATCH v3 1/1] net: fec: add xdp and page pool statist=
ics
>=20
> Caution: EXT Email
>=20
> > Drivers should never select PAGE_POOL_STATS. This Kconfig option was
> > made to allow user to choose whether he wants stats or better
> > performance on slower systems. It's pure user choice, if something
> > doesn't build or link, it must be guarded with
> > IS_ENABLED(CONFIG_PAGE_POOL_STATS).
>=20
> Given how simple the API is, and the stubs for when CONFIG_PAGE_POOL_STAT=
S
> is disabled, i doubt there is any need for the driver to do anything.
>=20
> > >     struct page_pool *page_pool;
> > >     struct xdp_rxq_info xdp_rxq;
> > > +   u32 stats[XDP_STATS_TOTAL];
> >
> > Still not convinced it is okay to deliberately provoke overflows here,
> > maybe we need some more reviewers to help us agree on what is better?
>=20
> You will find that many embedded drivers only have 32 bit hardware stats =
and do
> wrap around. And the hardware does not have atomic read and clear so you =
can
> accumulate into a u64. The FEC is from the times of MIB 2 ifTable, which =
only
> requires 32 bit counters. ifXtable is modern compared to the FEC.
>=20
> Software counters like this are a different matter. The overhead of a
> u64 on a 32 bit system is probably in the noise, so i think there is stro=
ng
> argument for using u64.

If it is required to support u64 counters, the code logic need to change to=
 record=20
the counter locally per packet, and then update the counters for the fec in=
stance
when the napi receive loop is complete. In this way we can reduce the perfo=
rmance
overhead.

Thanks,
Shenwei

>=20
>        Andrew