linux-kernel - Re: [PATCH v2] tcp: splice as many packets as possible at once

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: <20090204192820.GA27867@1wt.eu>
Date:	Wed, 4 Feb 2009 20:28:20 +0100
From:	Willy Tarreau <w@....eu>
To:	Roland Dreier <rdreier@...co.com>
Cc:	David Miller <davem@...emloft.net>, herbert@...dor.apana.org.au,
	zbr@...emap.net, jarkao2@...il.com, dada1@...mosbay.com,
	ben@...s.com, mingo@...e.hu, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org, jens.axboe@...cle.com
Subject: Re: [PATCH v2] tcp: splice as many packets as possible at once

On Wed, Feb 04, 2009 at 11:19:06AM -0800, Roland Dreier wrote:
>  > And the arbitrary choice of 9k for jumbo frames was total crap too.
>  > It's clear that no hardware designer was involved in the process.
>  > They have to stuff 16kB of RAM on a NIC to use only 9. And we need
>  > to allocate 3 pages for slightly more than 2. 7.5 kB would have been
>  > better in this regard.
> 
> 9K was not totally arbitrary.  The CRC used for checksumming ethernet
> packets has a probability of undetected errors that goes up about
> 11-thousand something bytes.  So the real limit is ~11000 bytes, and I
> believe ~9000 was chosen to be able to carry 8K NFS payloads + all XDR
> and transport headers without fragmentation.

Yes I know that initial motivation. But IMHO it was a purely functional
motivation without real considerations of the implications. When you
read Alteon's initial proposal, there is even a biased analysis (they
compare the fill ratio obtained with one 8k frame with that of 6 1.5k
frames). Their own argument does not stand with their final proposal!
I think that there might already have been people pushing for 8k and
not 9 by then, but in order to get wide acceptance in datacenters,
they had to please the NFS admins.

Now it's useless to speculate on history and I agree with Davem that
we're wasting our time with this discussion, let's go back to the
keyboard ;-)

Willy

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/