netdev - Re: [PATCH net-next v2] net/sched: act_police: add support for packet-per-second policing

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Date:   Fri, 29 Jan 2021 15:04:51 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Simon Horman <simon.horman@...ronome.com>
Cc:     David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Jiri Pirko <jiri@...lanox.com>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        oss-drivers@...ronome.com, Baowen Zheng <baowen.zheng@...igine.com>
Subject: Re: [PATCH net-next v2] net/sched: act_police: add support for
 packet-per-second policing

On Fri, Jan 29, 2021 at 2:29 AM Simon Horman <simon.horman@...ronome.com> wrote:
> +/**
> + * psched_ratecfg_precompute__() - Pre-compute values for reciprocal division
> + * @rate:   Rate to compute reciprocal division values of
> + * @mult:   Multiplier for reciprocal division
> + * @shift:  Shift for reciprocal division
> + *
> + * The multiplier and shift for reciprocal division by rate are stored
> + * in mult and shift.
> + *
> + * The deal here is to replace a divide by a reciprocal one
> + * in fast path (a reciprocal divide is a multiply and a shift)
> + *
> + * Normal formula would be :
> + *  time_in_ns = (NSEC_PER_SEC * len) / rate_bps
> + *
> + * We compute mult/shift to use instead :
> + *  time_in_ns = (len * mult) >> shift;
> + *
> + * We try to get the highest possible mult value for accuracy,
> + * but have to make sure no overflows will ever happen.
> + *
> + * reciprocal_value() is not used here it doesn't handle 64-bit values.
> + */
> +static void psched_ratecfg_precompute__(u64 rate, u32 *mult, u8 *shift)

Am I the only one who thinks "foo__()" is an odd name? We usually use
"__foo()" for helper or unlocked version of "foo()".

And, you probably want to move the function doc to its exported variant
instead, right?

Thanks.