netdev - Re: [Bloat] tc linklayer ADSL calc broken after commit 56b765b79 (htb: improved accuracy at high rates)

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Thu, 30 May 2013 11:52:53 +0200
From:	"Steinar H. Gunderson" <sgunderson@...foot.com>
To:	Jesper Dangaard Brouer <jbrouer@...hat.com>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	Toke Høiland-Jørgensen <toke@...e.dk>,
	Mike Frysinger <vapier@...too.org>,
	Jiri Benc <jbenc@...hat.com>, Jiri Pirko <jpirko@...hat.com>,
	netdev@...r.kernel.org, bloat@...ts.bufferbloat.net,
	Patrick McHardy <kaber@...sh.net>,
	Steven Barth <cyrus@...nwrt.org>,
	"russell-tcatm@...art.id.au" <russell-tcatm@...art.id.au>,
	David Miller <davem@...hat.com>,
	Jussi Kivilinna <jussi.kivilinna@...et.fi>,
	Felix Fietkau <nbd@....name>, Michal Soltys <soltys@....info>
Subject: Re: [Bloat] tc linklayer ADSL calc broken after commit 56b765b79
 (htb: improved accuracy at high rates)

On Thu, May 30, 2013 at 11:15:47AM +0200, Jesper Dangaard Brouer wrote:
>  int pkt_len = skb->len + (encap_overhead * gso_segments);
>  int wire_sz = DIV_ROUND_UP(pkt_len,48)*53;
> 
> (I suspect, that the compiler might even optimize and remove any
> real divisions, I bet Eric can tell us.)

FWIW, GCC can change divisions by integer constants (even signed divisions)
to some multiplies and shifts, by way of some number theory magic.

/* Steinar */
-- 
Homepage: http://www.sesse.net/
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html