From mboxrd@z Thu Jan  1 00:00:00 1970
From: Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= <toke@toke.dk>
Subject: Re: [PATCH 3/4] sch_api: Allow reducing queue backlog by a negative value
Date: Tue, 08 Jan 2019 10:55:51 +0100
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References: <20190107194733.31138-1-toke@toke.dk> <20190107194733.31138-4-toke@toke.dk> <69d53b63-f7ed-3c6e-f191-43ec7fbd1735@gmail.com>
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Cc: cake@lists.bufferbloat.net,
        Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= <toke@redhat.com>
To: Eric Dumazet <eric.dumazet@gmail.com>, netdev@vger.kernel.org
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Eric Dumazet <eric.dumazet@gmail.com> writes:

> On 01/07/2019 11:47 AM, Toke H=C3=B8iland-J=C3=B8rgensen wrote:
>> From: Toke H=C3=B8iland-J=C3=B8rgensen <toke@redhat.com>
>>=20
>> 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 -=3D n;
> sch->qstats.backlog -=3D 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