linux-kernel - Re: [PATCH 1/7] [NET]: uninline skb

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Date:	Thu, 27 Mar 2008 17:54:40 -0700
From:	Joe Perches <joe@...ches.com>
To:	Matt Mackall <mpm@...enic.com>
Cc:	David Miller <davem@...emloft.net>, ilpo.jarvinen@...sinki.fi,
	akpm@...ux-foundation.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, acme@...hat.com
Subject: Re: [PATCH 1/7] [NET]: uninline skb_put, de-bloats a lot

On Thu, 2008-03-27 at 19:11 -0500, Matt Mackall wrote:
> In the 486 era, when CPU performance was close to 1:1 with memory,
> branches were more expensive than sequential memory fetches, and
> registers were scarce, inlining made a fair amount of sense.
> 
> But now we've moved very far away from that indeed:

Systems have certainly improved but Linux is used in a
wide variety of CPU Hz, memory & register architectures.

Some of those systems haven't changed at all.
Some of those systems have sufficient cache for a
networking stack.

I think this change could negatively impact some of these
different uses and systems.

> In the case of this patch, removing 60-100k from the network stack means
> we're almost certainly avoiding a lot of cache misses in the big picture
> while taking a few cycle hit per packet in the smallest scale.

I think the quantities of big v small are instance dependent
and it might be prudent to have the capability to keep these
functions inline.

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