Date:   Wed, 15 Mar 2023 14:33:27 +0100
From:   'Horatiu Vultur' <horatiu.vultur@microchip.com>
To:     David Laight <David.Laight@aculab.com>
CC:     "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "davem@davemloft.net" <davem@davemloft.net>,
        "edumazet@google.com" <edumazet@google.com>,
        "kuba@kernel.org" <kuba@kernel.org>,
        "pabeni@redhat.com" <pabeni@redhat.com>,
        "richardcochran@gmail.com" <richardcochran@gmail.com>,
        "UNGLinuxDriver@microchip.com" <UNGLinuxDriver@microchip.com>
Subject: Re: [PATCH net-next 2/2] net: lan966x: Stop using packing library
Message-ID: <20230315133327.akf4lkdxt67eh3nd@soft-dev3-1>
References: <20230312202424.1495439-1-horatiu.vultur@microchip.com>
 <20230312202424.1495439-3-horatiu.vultur@microchip.com>
 <cad1c4aac9ae4047b8ed29b181c908fd@AcuMS.aculab.com>
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The 03/13/2023 17:04, David Laight wrote:
> 
> From: Horatiu Vultur
> > Sent: 12 March 2023 20:24
> >
> > When a frame is injected from CPU, it is required to create an IFH(Inter
> > frame header) which sits in front of the frame that is transmitted.
> > This IFH, contains different fields like destination port, to bypass the
> > analyzer, priotity, etc. Lan966x it is using packing library to set and
> > get the fields of this IFH. But this seems to be an expensive
> > operations.
> > If this is changed with a simpler implementation, the RX will be
> > improved with ~5Mbit while on the TX is a much bigger improvement as it
> > is required to set more fields. Below are the numbers for TX.
> ...
> > +static void lan966x_ifh_set(u8 *ifh, size_t val, size_t pos, size_t length)
> > +{
> > +     u32 v = 0;
> > +
> > +     for (int i = 0; i < length ; i++) {
> > +             int j = pos + i;
> > +             int k = j % 8;
> > +
> > +             if (i == 0 || k == 0)
> > +                     v = ifh[IFH_LEN_BYTES - (j / 8) - 1];
> > +
> > +             if (val & (1 << i))
> > +                     v |= (1 << k);
> > +
> > +             if (i == (length - 1) || k == 7)
> > +                     ifh[IFH_LEN_BYTES - (j / 8) - 1] = v;
> > +     }
> > +}
> > +
> 
> It has to be possible to do much better that that.
> Given  that 'pos' and 'length' are always constants it looks like
> each call should reduce to (something like):
>         ifh[k] |= val << n;
>         ifk[k + 1] |= val >> (8 - n);
>         ...
> It might be that the compiler manages to do this, but I doubt it.

Thanks for the review. I will update this in the next version.

Do you think it is worth updating the code in lan966x_ifh_get to use
byte access and not to read each bit individually?
As there is no much improvement on the RX side that is using lan966x_ifh_get.

> 
>         David
> 
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
> Registration No: 1397386 (Wales)
> 

-- 
/Horatiu