From: Andi Kleen <andi@firstfloor.org>
To: William Allen Simpson <william.allen.simpson@gmail.com>
Cc: "Linux Kernel Developers" <linux-kernel@vger.kernel.org>,
"Linux Kernel Network Developers" <netdev@vger.kernel.org>,
"Ilpo Järvinen" <ilpo.jarvinen@helsinki.fi>,
"Eric Dumazet" <eric.dumazet@gmail.com>,
"Andi Kleen" <andi@firstfloor.org>
Subject: Re: [PATCH v4] tcp: harmonize tcp_vx_rcv header length assumptions
Date: Wed, 13 Jan 2010 12:56:17 +0100 [thread overview]
Message-ID: <20100113115617.GA24818@basil.fritz.box> (raw)
In-Reply-To: <4B4DA4F4.6060007@gmail.com>
On Wed, Jan 13, 2010 at 05:48:20AM -0500, William Allen Simpson wrote:
> Harmonize tcp_v4_rcv() and tcp_v6_rcv() -- better document tcp doff
> and header length assumptions.
>
> Reduces multiply/shifts, marginally improving speed.
>
> Removes redundant tcp header length checks before checksumming.
I wonder if this actually improves performance on x86. On x86 and several
other architecture there's a addressing mode which allows to scale
numbers by small factors (like 4). So doing a *4 is very cheap.
That's likely cheaper than using another register for the scaled value,
especially on 32bit x86 which doesn't have many.
It's difficult to benchmark this code, but did you check that the code
shrinks after applying this patch at least?
-andi
next prev parent reply other threads:[~2010-01-13 11:56 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-01-10 13:02 query: redundant tcp header length checks? William Allen Simpson
2010-01-12 10:05 ` [PATCH] tcp: harmonize tcp_vx_rcv header length assumptions William Allen Simpson
2010-01-12 10:46 ` Eric Dumazet
2010-01-12 17:11 ` William Allen Simpson
2010-01-13 9:50 ` William Allen Simpson
2010-01-12 17:14 ` William Allen Simpson
2010-01-13 10:48 ` [PATCH v4] " William Allen Simpson
2010-01-13 11:56 ` Andi Kleen [this message]
2010-01-13 15:36 ` William Allen Simpson
2010-01-13 15:53 ` Andi Kleen
2010-01-13 16:40 ` [PATCH] Makefile: Document ability to make file.lst and file.S Joe Perches
2010-01-13 17:14 ` Andi Kleen
2010-01-13 17:31 ` Joe Perches
2010-01-13 19:51 ` William Allen Simpson
2010-01-14 3:26 ` Américo Wang
2010-01-18 12:29 ` Michal Marek
2010-01-13 19:49 ` [PATCH v4] tcp: harmonize tcp_vx_rcv header length assumptions William Allen Simpson
2010-01-13 20:19 ` Andi Kleen
2010-01-13 21:13 ` William Allen Simpson
2010-01-14 1:03 ` Joe Perches
2010-01-14 8:39 ` Patrick McHardy
2010-01-14 15:02 ` William Allen Simpson
2010-01-14 15:10 ` [PATCH v5] " William Allen Simpson
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