netdev - Re: [PATCH 3/4] sch_api: Allow reducing queue backlog by a negative value

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Date:   Tue, 08 Jan 2019 10:55:51 +0100
From:   Toke Høiland-Jørgensen <toke@...e.dk>
To:     Eric Dumazet <eric.dumazet@...il.com>, netdev@...r.kernel.org
Cc:     cake@...ts.bufferbloat.net,
        Toke Høiland-Jørgensen <toke@...hat.com>
Subject: Re: [PATCH 3/4] sch_api: Allow reducing queue backlog by a negative value

Eric Dumazet <eric.dumazet@...il.com> writes:

> On 01/07/2019 11:47 AM, Toke Høiland-Jørgensen wrote:
>> From: Toke Høiland-Jørgensen <toke@...hat.com>
>> 
>> With GSO splitting in sch_cake, we can decrease as well as increase the
>> qlen. To make it possible to signal this up the qdisc tree, change
>> qdisc_tree_reduce_backlog() to accept signed integer values as the number
>> of packets and bytes to reduce the backlog by.
>
>
> Not sure why this patch is needed, given we use u32 integers
> for q.qlen & qstats.backlog
>
> 0xFFFFFFFF for n is really -1 once folded...
>
> sch->q.qlen -= n;
> sch->qstats.backlog -= len;

Sure, it works without the patch, but changing to int properly
communicates the intent (that negative values are allowed) rather than
rely on overflow behaviour...

-Toke