netdev - Re: [PATCH net] pktgen: Fix the inaccurate bps calculation

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Date:   Fri, 8 Jul 2022 17:59:42 +0200
From:   Eric Dumazet <edumazet@...gle.com>
To:     gfree.wind@...look.com
Cc:     David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        netdev <netdev@...r.kernel.org>, Gao Feng <gfree.wind@...il.com>
Subject: Re: [PATCH net] pktgen: Fix the inaccurate bps calculation

On Fri, Jul 8, 2022 at 5:14 PM <gfree.wind@...look.com> wrote:
>
> From: Gao Feng <gfree.wind@...il.com>
>
> The prior codes use 1000000 as divisor to convert to the Mbps. But it isn't
> accurate, because the NIC uses 1024*1024 from bps to Mbps. The result of
> the codes is 1.05 times as the real value, even it may cause the result is
> more than the nic's physical rate.


1Mbit = 1,000,000 bits per second.

https://en.wikipedia.org/wiki/Megabit

Current code is right IMO.

>
> Signed-off-by: Gao Feng <gfree.wind@...il.com>
> ---
>  net/core/pktgen.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/net/core/pktgen.c b/net/core/pktgen.c
> index 84b62cd7bc57..e5cd3da63035 100644
> --- a/net/core/pktgen.c
> +++ b/net/core/pktgen.c
> @@ -3305,7 +3305,7 @@ static void show_results(struct pktgen_dev *pkt_dev, int nr_frags)
>         }
>
>         mbps = bps;
> -       do_div(mbps, 1000000);
> +       do_div(mbps, 1024 * 1024);
>         p += sprintf(p, "  %llupps %lluMb/sec (%llubps) errors: %llu",
>                      (unsigned long long)pps,
>                      (unsigned long long)mbps,
> --
> 2.20.1
>