linux-kernel - Re: [PATCH 0/2] ARM: omap2+: omap_hwmod: Fix false lockdep warning

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Message-ID: <alpine.DEB.2.02.1502091557450.3767@utopia.booyaka.com>
Date:	Mon, 9 Feb 2015 16:00:55 +0000 (UTC)
From:	Paul Walmsley <paul@...an.com>
To:	Peter Ujfalusi <peter.ujfalusi@...com>
cc:	Peter Zijlstra <peterz@...radead.org>,
	Tony Lindgren <tony@...mide.com>, linux-omap@...r.kernel.org,
	mingo@...hat.com, linux-kernel@...r.kernel.org, balbi@...com,
	linux-arm-kernel@...ts.infradead.org, Tero Kristo <t-kristo@...com>
Subject: Re: [PATCH 0/2] ARM: omap2+: omap_hwmod: Fix false lockdep warning

On Mon, 9 Feb 2015, Peter Ujfalusi wrote:

> On 02/06/2015 09:26 PM, Peter Ujfalusi wrote:
> >> Yeah, I've never really bothered with data too much, its a debug
> >> feature. So lock_class_key is 8 bytes, and strictly speaking you could
> >> union them over other fields, all we really need is unique addresses, we
> >> don't actually use the storage.
> > 
> > True. our omap2plus defconfig does not have LOCKDEP enabled so it should not
> > add anything to the data when running default kernel.
> > I'll test the lockdep_set_class() method you suggested on Monday (not
> > tomorrow), but still as first thing.
> > If it is working as expected I'll send a patch with you as author.
> 
> With omap2plus_defconfig my build produces (vmlinux size):
> Base: 				99905522
> with my series:			99908385 (base + 2863)
> with Peter Zijlstra's patch:	99910625 (base + 5103)
> 
> The reason for this is that we will only have
> struct lock_class_key { };
> in case of !CONFIG_LOCKDEP. On ARM however CONFIG_LOCKDEP is enabled by
> default, while the CONFIG_DEBUG_LOCKDEP is disabled.
> 
> So it does add more data to our default omap2plus config.
> 
> Tony: do you have preference on the way we fix this issue?
> 
> As I recall there is a plan to remove the hwmod static database and move it or
> generate it from DT? Not sure when and how this will be done, but will it
> affect the lockdep_set_class() way?

Well I guess we could see what Tony says, but you do realize that the 
difference in sizes that you posted above is about .003% of the total 
binary size, right?  

If there's one thing we can say about the last few years of ARM kernel 
development, it's that those kind of size increases are utterly dwarfed by 
other changes in the kernel.  So I'd say, post a patch based on PeterZ's 
fix and be done with it...


- Paul
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