From: Stephen Hemminger <shemminger@vyatta.com>
To: Eric Dumazet <eric.dumazet@gmail.com>
Cc: David Miller <davem@davemloft.net>,
netdev <netdev@vger.kernel.org>, Florian Westphal <fw@strlen.de>,
Patrick McHardy <kaber@trash.net>,
Hagen Paul Pfeifer <hagen@jauu.net>,
Jarek Poplawski <jarkao2@gmail.com>
Subject: Re: [BUG] net_sched: pfifo_head_drop problem
Date: Wed, 5 Jan 2011 09:15:47 -0800 [thread overview]
Message-ID: <20110105091547.200b49ad@nehalam> (raw)
In-Reply-To: <1294246850.2775.244.camel@edumazet-laptop>
On Wed, 05 Jan 2011 18:00:50 +0100
Eric Dumazet <eric.dumazet@gmail.com> wrote:
> While reviewing CHOKe stuff, I found following problem :
>
> commit 57dbb2d83d100ea (sched: add head drop fifo queue)
> introduced pfifo_head_drop, and broke the invariant that
> sch->bstats.bytes and sch->bstats.packets are COUNTER (increasing
> counters only)
>
> This can break estimators because est_timer() handle unsigned deltas
> only. A decreasing counter can then give a huge unsigned delta.
>
> My suggestion would be to change things so that sch->bstats.bytes and
> sch->bstats.packets are incremented in dequeue() only, not at enqueue()
> time.
>
> It would be more sensible anyway for very low speeds, and big bursts.
> Right now, if we drop packets, they still are accounted in estimators.
>
> Or maybe my understanding of estimators is wrong, and only apply to
> enqueue rate, not dequeue rate ?
>
> If so, we should remove the
>
> sch->bstats.bytes -= qdisc_pkt_len(skb_head);
> sch->bstats.packets--;
>
> done in pfifo_tail_enqueue() in case we drop the head skb.
>
>
> My preference would be to add dropped pack/byte rates to estimators...
> It might be good for tuning.
Agreed counters should reflect dequeued packets not enqueued packets.
--
next prev parent reply other threads:[~2011-01-05 17:15 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-01-05 17:00 [BUG] net_sched: pfifo_head_drop problem Eric Dumazet
2011-01-05 17:15 ` Stephen Hemminger [this message]
2011-01-05 20:35 ` [PATCH] " Eric Dumazet
2011-01-05 20:52 ` Hagen Paul Pfeifer
2011-01-05 21:39 ` David Miller
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20110105091547.200b49ad@nehalam \
--to=shemminger@vyatta.com \
--cc=davem@davemloft.net \
--cc=eric.dumazet@gmail.com \
--cc=fw@strlen.de \
--cc=hagen@jauu.net \
--cc=jarkao2@gmail.com \
--cc=kaber@trash.net \
--cc=netdev@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).