linux-kernel - Re: [PATCH 2/2] powerpc: Switch to generic WARN_ON()/BUG

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Date:	Thu, 11 Oct 2007 21:41:43 -0500
From:	Olof Johansson <olof@...om.net>
To:	Kyle McMartin <kyle@...artin.ca>
Cc:	Paul Mackerras <paulus@...ba.org>, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, lethal@...ux-sh.org,
	kyle@...isc-linux.org, grundler@...isc-linux.org,
	linuxppc-dev@...abs.org
Subject: Re: [PATCH 2/2] powerpc: Switch to generic WARN_ON()/BUG_ON()

On Thu, Oct 11, 2007 at 10:04:19PM -0400, Kyle McMartin wrote:
> On Fri, Oct 12, 2007 at 11:23:39AM +1000, Paul Mackerras wrote:
> > Olof Johansson writes:
> > 
> > > Not using the ppc-specific WARN_ON/BUG_ON constructs actually saves about
> > > 4K text on a ppc64_defconfig. The main reason seems to be that prepping
> > > the arguments to the conditional trap instructions is more work than
> > > just doing a compare and branch.
> > 
> > It might be more instructions but it takes fewer cycles, I would
> > expect.  Do you have the actual instruction sequences to compare?
> > 
> 
> I really hope WARN_ON/BUG_ON aren't hotpaths on powerpc. ;-)

Not the taken branch of them, no. :)  But making it past them as fast
as possible when they're not tripping is always good.


-Olof
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