From: Cong Wang <xiyou.wangcong@gmail.com>
To: Jakub Kicinski <jakub.kicinski@netronome.com>
Cc: David Miller <davem@davemloft.net>,
Linux Kernel Network Developers <netdev@vger.kernel.org>,
oss-drivers@netronome.com,
Stephen Hemminger <stephen@networkplumber.org>,
kbuild test robot <lkp@intel.com>,
Dan Carpenter <dan.carpenter@oracle.com>,
Ben Hutchings <ben@decadent.org.uk>,
Simon Horman <simon.horman@netronome.com>
Subject: Re: [PATCH net] net: netem: fix error path for corrupted GSO frames
Date: Thu, 17 Oct 2019 11:10:06 -0700 [thread overview]
Message-ID: <CAM_iQpW=S+UarEKCtL6q_ZyxVn0chVLgXQyfRNP_Kw-P8_Qt+Q@mail.gmail.com> (raw)
In-Reply-To: <20191016162210.5f2a8256@cakuba.netronome.com>
On Wed, Oct 16, 2019 at 4:22 PM Jakub Kicinski
<jakub.kicinski@netronome.com> wrote:
>
> On Wed, 16 Oct 2019 15:42:28 -0700, Cong Wang wrote:
> > > @@ -612,7 +613,7 @@ static int netem_enqueue(struct sk_buff *skb, struct Qdisc *sch,
> > > }
> > > segs = skb2;
> > > }
> > > - qdisc_tree_reduce_backlog(sch, -nb, prev_len - len);
> > > + qdisc_tree_reduce_backlog(sch, !skb - nb, prev_len - len);
> >
> > Am I the only one has trouble to understand the expression
> > "!skb - nb"?
>
> The backward logic of qdisc_tree_reduce_backlog() always gives me a
> pause :S
Yeah, reducing with a negative value is actually an add. Feel free
to add a wrapper for this if you think it is better.
>
> Is
> -nb + !skb
> any better?
I don't see how they are different. :-/
>
> The point is we have a "credit" for the "head" skb we dropped. If we
> didn't manage to queue any of the segs then the expression becomes
> ...reduce_backlog(sch, 1, prev_len) basically cleaning up after the
> head.
>
> My knee jerk reaction was -> we should return DROP if head got dropped,
> but that just makes things more nasty because we requeue the segs
> directly into netem so if we say DROP we have to special case all the
> segs which succeeded, that gets even more hairy.
Hmm? My understanding is that !skb is either 0 or 1, so you end up
with either "-nb" or "1 - nb". The formal is easy to understand, while
the later is harder as I don't see why you need to plus 1.
>
> I'm open to suggestions.. :(
Why not write the code in a more readable way, for instance with the :?
operator? And, adding a comment in the code?
Thanks.
next prev parent reply other threads:[~2019-10-17 18:10 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-16 16:00 [PATCH net] net: netem: fix error path for corrupted GSO frames Jakub Kicinski
2019-10-16 22:42 ` Cong Wang
2019-10-16 23:22 ` Jakub Kicinski
2019-10-17 18:10 ` Cong Wang [this message]
2019-10-17 18:44 ` Jakub Kicinski
2019-10-17 19:28 ` Cong Wang
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