netdev - RE: [PATCH net-next] loopback: sctp: add NETIF_F_SCTP

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: Windows password security audit tool. GUI, reports in PDF.

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

Message-ID: <063D6719AE5E284EB5DD2968C1650D6D0F6C99F9@AcuExch.aculab.com>
Date:	Mon, 24 Feb 2014 13:24:58 +0000
From:	David Laight <David.Laight@...LAB.COM>
To:	'Daniel Borkmann' <dborkman@...hat.com>
CC:	"davem@...emloft.net" <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-sctp@...r.kernel.org" <linux-sctp@...r.kernel.org>
Subject: RE: [PATCH net-next] loopback: sctp: add NETIF_F_SCTP_CSUM to
 device features

From: Daniel Borkmann
> On 02/24/2014 11:42 AM, David Laight wrote:
> ...
> > I'm sure it shouldn't be that expensive, you are implying that it spent
> > about 70% of the time doing crc32.
> 
> In this scenario, the following perf log I get that shows where cycles
> are being spent on my machine:
> 
>   65.95%       netperf  [kernel.kallsyms]  [k] __crc32c_le

WTF is that function doing!
Even doing the crc naively bit by bit shouldn't manage to use 65%.

Maybe the _le has something to do with it.
Could it be bit-reversing the crc and data bytes all the time?
The packet will (one would hope) want the crc in the same bit-order
as the data, so no bit reversal is needed - just the correct logic
and lookup table.

Which architecture and which version of crc32_le() does your kernel use?
(I'd guess there are several lurking).
Whichever function you are using wants killing.

	David

--
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