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Date:   Thu, 12 Oct 2017 19:42:33 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Vinicius Costa Gomes <vinicius.gomes@...el.com>
Cc:     netdev@...r.kernel.org, intel-wired-lan@...ts.osuosl.org,
        jhs@...atatu.com, xiyou.wangcong@...il.com, jiri@...nulli.us,
        andre.guedes@...el.com, ivan.briano@...el.com,
        jesus.sanchez-palencia@...el.com, boon.leong.ong@...el.com,
        richardcochran@...il.com, henrik@...tad.us, levipearson@...il.com,
        rodney.cummings@...com
Subject: Re: [next-queue PATCH v7 4/6] net/sched: Introduce Credit Based
 Shaper (CBS) qdisc

On Thu, 2017-10-12 at 17:40 -0700, Vinicius Costa Gomes wrote:
> This queueing discipline implements the shaper algorithm defined by
> the 802.1Q-2014 Section 8.6.8.2 and detailed in Annex L.
> 
> It's primary usage is to apply some bandwidth reservation to user
> defined traffic classes, which are mapped to different queues via the
> mqprio qdisc.
> 
> Only a simple software implementation is added for now.
> 
> Signed-off-by: Vinicius Costa Gomes <vinicius.gomes@...el.com>
> Signed-off-by: Jesus Sanchez-Palencia <jesus.sanchez-palencia@...el.com>
> ---

> +/* timediff is in ns, slope is in kbps */
> +static s64 timediff_to_credits(s64 timediff, s32 slope)
> +{
> +	s64 credits = timediff * slope * BYTES_PER_KBIT;
> +
> +	do_div(credits, NSEC_PER_SEC);
> +
> +	return credits;
> +}
> +
> +static s64 delay_from_credits(s64 credits, s32 slope)
> +{
> +	s64 rate = slope * BYTES_PER_KBIT;
> +	s64 delay;
> +
> +	if (unlikely(rate == 0))
> +		return S64_MAX;
> +
> +	delay = -credits * NSEC_PER_SEC;
> +	do_div(delay, rate);
> +
> +	return delay;
> +}
> +
> +static s64 credits_from_len(unsigned int len, s32 slope, s64 port_rate)
> +{
> +	/* As do_div() only works on unsigned quantities, convert
> +	 * slope to a positive number here, and credits to a negative
> +	 * number before returning.
> +	 */
> +	s64 rate = -slope * BYTES_PER_KBIT;
> +	s64 credits;
> +
> +	if (unlikely(port_rate == 0))
> +		return S64_MAX;
> +
> +	credits = len * rate;
> +	do_div(credits, port_rate);
> +
> +	return -credits;
> +}
> +


Your mixing of s64 and u64 is disturbing.

do_div() handles u64, not s64.

div64_s64() might be needed in place of do_div()



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