netdev - Re: [PATCH v2] net: filter: Just In Time compiler

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Date:	Thu, 14 Apr 2011 18:05:47 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Avi Kivity <avi@...hat.com>
Cc:	Hagen Paul Pfeifer <hagen@...u.net>,
	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Ben Hutchings <bhutchings@...arflare.com>
Subject: Re: [PATCH v2] net: filter: Just In Time compiler

Le jeudi 14 avril 2011 à 18:53 +0300, Avi Kivity a écrit :

> IMO, it will.  I'll try to have gcc optimize your example filter later.

Sure you can JIT a C program from bpf. It should take maybe 30 minutes.
It certainly is more easy than JIT an binary/assembly code :)

Now take a look how I call slowpath, I am not sure gcc will actually
generate better code because of C conventions.

Loading a filter should be fast.
Invoking a compiler is just too much work for BPF.
Remember loading a filter is available to any user.

This idea would be good for netfilter stuff, because we dont load
iptables rules that often.

But still, the netfilter mainloop can be converted as a kernel JIT, most
probably. All the complex stuff (matches, targets) must call external
procedures anyway.

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