netdev - Re: multi bpf filter will impact performance?

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Date:	Fri, 03 Dec 2010 07:32:33 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	hagen@...u.net, xiaosuo@...il.com, wirelesser@...il.com,
	netdev@...r.kernel.org
Subject: Re: multi bpf filter will impact performance?

Le mercredi 01 décembre 2010 à 10:18 -0800, David Miller a écrit :

> However, I think it's still valuable to write a few JIT compilers for
> the existing BPF stuff.  I considered working on a sparc64 JIT just to
> see what it would look like.
> 
> If people work on the BPF optimizer and BPF JITs in parallel, we'll have
> both ready at the same time.  win++

I began work on implementing a BPF JIT for x86_64

My plan is to use external helpers to load skb data/metadata, to keep
BPF program very short and have no dependencies against struct layouts.

These helpers would be the three load_word, load_half, load_byte.

In case the bits are in skb head, these helpers should be fast.

For practical reasons, they would be in ASM for their fast path, and C
for the slow path. They are ASM because they are able to perform the
shortcut (in case of error, doing the stack unwind to perform the
"return 0;") so that we dont have to test their return from the JIT
program.

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