netdev - Re: [PATCH v2] ARM: net: JIT compiler for packet filters

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Date:	Mon, 19 Dec 2011 15:24:18 +0000
From:	Dave Martin <dave.martin@...aro.org>
To:	Uwe Kleine-K?nig <u.kleine-koenig@...gutronix.de>
Cc:	Mircea Gherzan <mgherzan@...il.com>, netdev@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2] ARM: net: JIT compiler for packet filters

On Mon, Dec 19, 2011 at 04:19:58PM +0100, Uwe Kleine-K?nig wrote:
> On Mon, Dec 19, 2011 at 12:50:21PM +0000, Dave Martin wrote:
> > On Mon, Dec 19, 2011 at 09:40:30AM +0100, Mircea Gherzan wrote:
> > > Based of Matt Evans's PPC64 implementation.
> > > 
> > > Supports only ARM mode with EABI.
> > > 
> > > Supports both little and big endian. Depends on the support for
> > > unaligned loads on ARMv7. Does not support all the BPF opcodes
> > > that deal with ancillary data. The scratch memory of the filter
> > > lives on the stack.
> > > 
> > > Enabled in the same way as for x86-64 and PPC64:
> > > 
> > > 	echo 1 > /proc/sys/net/core/bpf_jit_enable
> > > 
> > > A value greater than 1 enables opcode output.
> > > 
> > > Signed-off-by: Mircea Gherzan <mgherzan@...il.com>
> > > ---
> > 
> > Interesting patch... I haven't reviewed in detail, but I have a few
> > quick comments.
> > 
> > > 
> > > Changes in v2:
> > >  * enable the compiler ony for ARMv5+ because of the BLX instruction
> > >  * use the same comparison for the ARM version checks
> > >  * use misaligned accesses on ARMv6
> > 
> > You probably want to change the commit message now to reflect this.
> > 
> > >  * fix the SEEN_MEM
> > >  * fix the mem_words_used()
> > > 
> > >  arch/arm/Kconfig          |    1 +
> > >  arch/arm/Makefile         |    1 +
> > >  arch/arm/net/Makefile     |    3 +
> > >  arch/arm/net/bpf_jit_32.c |  838 +++++++++++++++++++++++++++++++++++++++++++++
> > >  arch/arm/net/bpf_jit_32.h |  174 ++++++++++
> > >  5 files changed, 1017 insertions(+), 0 deletions(-)
> > >  create mode 100644 arch/arm/net/Makefile
> > >  create mode 100644 arch/arm/net/bpf_jit_32.c
> > >  create mode 100644 arch/arm/net/bpf_jit_32.h
> > > 
> > > diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> > > index abba5b8..ea65c41 100644
> > > --- a/arch/arm/Kconfig
> > > +++ b/arch/arm/Kconfig
> > > @@ -30,6 +30,7 @@ config ARM
> > >  	select HAVE_SPARSE_IRQ
> > >  	select GENERIC_IRQ_SHOW
> > >  	select CPU_PM if (SUSPEND || CPU_IDLE)
> > > +	select HAVE_BPF_JIT if (!THUMB2_KERNEL && AEABI)
> > 
> > Have to tried your code with a Thumb-2 kernel?
> > 
> > Quickly skimming though your patch, I don't see an obvious reason why we
> > can't have that working, though I haven't tried it yet.
> > 
> > Note that it's fine to have the JIT generating ARM code, even if the rest
> > if the kernel is Thumb-2.  This would only start to cause problems if we
> > want to do things like set kprobes in the JITted code, or unwind out of
> > the JITted code.
> or use a CPU that doesn't speak ARM (e.g. v7M)

Indeed... I was assuming though that that would be out of scope for the
first iteration of this code.

Cheers
---Dave
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