netdev - Re: [PATCH net] bpf: do not use reciprocal divide

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Message-ID: <1389802077.31367.347.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Wed, 15 Jan 2014 08:07:57 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Martin Schwidefsky <schwidefsky@...ibm.com>
Cc:	Heiko Carstens <heiko.carstens@...ibm.com>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	netdev@...r.kernel.org, dborkman@...hat.com,
	darkjames-ws@...kjames.pl, Mircea Gherzan <mgherzan@...il.com>,
	Russell King <rmk+kernel@....linux.org.uk>,
	Matt Evans <matt@...abs.org>
Subject: Re: [PATCH net] bpf: do not use reciprocal divide

On Wed, 2014-01-15 at 16:26 +0100, Martin Schwidefsky wrote:

> The C compiler naturally can to a u32/u32 division, it either uses
> the "dlr" instruction which is unsigned, or uses a call to a function
> to do the u32/u32 math. See the lovely code in arch/s390/lib/div64.c
> for the kernel version of that code.

If the C code uses unsigned, then all arch jit code must use the same.

Behavior of the filter should not depend of jit being enabled or not ;)


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