From: Paolo Valente <paolo.valente@unimore.it>
To: David Miller <davem@davemloft.net>
Cc: jhs@mojatatu.com, shemminger@vyatta.com,
linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
rizzo@iet.unipi.it, fchecconi@gmail.com
Subject: Re: [PATCH] pkt_sched: QFQ Plus: fair-queueing service at DRR cost
Date: Wed, 21 Nov 2012 10:45:14 +0100 [thread overview]
Message-ID: <50ACA2AA.1020206@unimore.it> (raw)
In-Reply-To: <20121120.135409.1810847883436963918.davem@davemloft.net>
Il 20/11/2012 19:54, David Miller ha scritto:
> From: Paolo Valente <paolo.valente@unimore.it>
> Date: Tue, 20 Nov 2012 18:45:13 +0100
>
>> - struct sk_buff *skb;
>> + struct sk_buff *skb = NULL;
>
> This is not really an improvement,
Sorry for trying this silly short cut
now the compiler can think
> that NULL is passed eventually into qdisc_bstats_update().
>
> Please make the logic easier for the compiler to digest.
>
> For example, restructure the top-level logic into something like:
>
> skb = NULL;
> if (!list_empty(&in_serv_agg->active))
> skb = qfq_peek_skb(in_serv_agg, &cl, &len);
> else
> len = 0; /* no more active classes in the in-service agg */
>
> if (len == 0 || in_serv_agg->budget < len) {
> ...
> /*
> * If we get here, there are other aggregates queued:
> * choose the new aggregate to serve.
> */
> in_serv_agg = q->in_serv_agg = qfq_choose_next_agg(q);
> skb = qfq_peek_skb(in_serv_agg, &cl, &len);
> }
> if (!skb)
> return NULL;
>
> That way it is clearer, to both humans and the compiler, what is
> going on here.
>
Got it. Actually, if the first qfq_peek_skb returns NULL, then the
example version that you are proposing apparently may behave in a
different way than the original one: in your proposal the scheduler
tries to switch to a new aggregate and may return a non-NULL value,
whereas the original version would immediately return NULL. I guess that
this slightly different behavior is fine as well, and I am preparing a
new patch that integrates these changes.
> Thanks.
>
--
-----------------------------------------------------------
| Paolo Valente | |
| Algogroup | |
| Dip. Ing. Informazione | tel: +39 059 2056318 |
| Via Vignolese 905/b | fax: +39 059 2056129 |
| 41125 Modena - Italy | |
| home: http://algo.ing.unimo.it/people/paolo/ |
-----------------------------------------------------------
next prev parent reply other threads:[~2012-11-21 9:45 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-11-20 17:45 [PATCH] pkt_sched: QFQ Plus: fair-queueing service at DRR cost Paolo Valente
2012-11-20 18:54 ` David Miller
2012-11-21 9:45 ` Paolo Valente [this message]
2012-11-21 17:04 ` David Miller
-- strict thread matches above, loose matches on Subject: below --
2012-11-23 21:03 Paolo Valente
2012-11-28 16:20 ` David Miller
2012-11-22 16:56 Paolo Valente
2012-11-23 19:28 ` David Miller
2012-11-23 21:02 ` Paolo Valente
2012-11-12 16:48 Paolo Valente
2012-11-19 23:48 ` David Miller
2012-11-20 17:45 ` Paolo Valente
2012-11-20 17:53 ` Stephen Hemminger
2012-11-20 18:02 ` David Miller
2012-11-20 18:09 ` Stephen Hemminger
2012-11-20 18:15 ` David Miller
2012-11-20 18:44 ` Stephen Hemminger
2012-11-20 18:00 ` 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=50ACA2AA.1020206@unimore.it \
--to=paolo.valente@unimore.it \
--cc=davem@davemloft.net \
--cc=fchecconi@gmail.com \
--cc=jhs@mojatatu.com \
--cc=linux-kernel@vger.kernel.org \
--cc=netdev@vger.kernel.org \
--cc=rizzo@iet.unipi.it \
--cc=shemminger@vyatta.com \
/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).