netdev - Re: [PATCH v2 net-next 1/3] netem: convert to qdisc_watchdog_schedule

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Date:   Wed, 08 Nov 2017 14:20:56 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Dave Taht <dave.taht@...il.com>
Cc:     netdev@...r.kernel.org, stephen@...workplumber.org
Subject: Re: [PATCH v2 net-next 1/3] netem: convert to
 qdisc_watchdog_schedule_ns

On Wed, 2017-11-08 at 13:09 -0800, Dave Taht wrote:
> Upgrade the internal netem scheduler to use nanoseconds rather than
> ticks throughout.
> 
...

> -static psched_time_t packet_len_2_sched_time(unsigned int len, struct netem_sched_data *q)
> +static s64 packet_len_2_sched_time(unsigned int len,
> +				   struct netem_sched_data *q)
>  {
> -	u64 ticks;
> -
> +	s64 offset;
>  	len += q->packet_overhead;
>  
>  	if (q->cell_size) {
> @@ -345,11 +345,9 @@ static psched_time_t packet_len_2_sched_time(unsigned int len, struct netem_sche
>  			cells++;
>  		len = cells * (q->cell_size + q->cell_overhead);
>  	}
> -
> -	ticks = (u64)len * NSEC_PER_SEC;
> -
> -	do_div(ticks, q->rate);
> -	return PSCHED_NS2TICKS(ticks);
> +	offset = (s64)len * NSEC_PER_SEC;
> +	do_div(offset, q->rate);
> +	return offset;
>  }

do_div() first argument being u64, I do not see why you chose 
's64 offset'

packet_len_2_sched_time() should return u64, because I do not see how we
could return a negative value, since a packet length is positive.