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From: Russell King - ARM Linux <linux@arm.linux.org.uk>
To: Michal Marek <mmarek@suse.cz>
Cc: Jason Cooper <jason@lakedaemon.net>,
	Linus Walleij <linus.walleij@linaro.org>,
	Grant Likely <grant.likely@secretlab.ca>,
	Rob Herring <rob.herring@linaro.org>,
	linux-kernel@vger.kernel.org, devicetree@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] ARM: kbuild: Fix forced rebuild after 'make dtbs'
Date: Tue, 25 Nov 2014 23:51:50 +0000	[thread overview]
Message-ID: <20141125235150.GH3836@n2100.arm.linux.org.uk> (raw)
In-Reply-To: <5474F78F.2060906@suse.cz>

On Tue, Nov 25, 2014 at 10:41:35PM +0100, Michal Marek wrote:
> Dne 2.11.2014 v 21:52 Jason Cooper napsal(a):
> > After this patch:
> > 
> >   f4d4ffc03efc kbuild: dtbs_install: new make target
> > 
> > was added the kernel tree, Linus Walleij noticed that 'make dtbs' forced
> > a following 'make zImage' to rebuild the entire tree, even though
> > nothing had changed.  His report:
> > 
> >   After this patch a while back I have observed the following behaviour
> >   of the kernel build:
> > 
> >   make zImage
> >   make zImage
> >   -> incremental build, just relink
> > 
> >   make zImage
> >   make dtbs
> >   make zImage
> >   -> The whole kernel gets rebuilt
> > 
> >   So now if I happen to recompile my device trees, I suddenly want
> >   the entire zImage to be rebuilt to? It's by definition not changes
> >   that affect the kernel build :-(
> > 
> >   I noticed this because my build scripts calls make dtbs && make
> >   zImage, and started to rebuild absolutely everything all the time.
> > 
> > To fix this, we make only the dtbs_install target depend on the prepare
> > target.  It's needed to make sure KERNELVERSION is calculated prior to
> > installing.
> 
> If a mere 'make prepare' causes a rebuild of the whole kernel, then
> there is something fishy in the ARM Makefiles. However, if you only need
> the KERNELRELEASE variable, then you do not need to depend on prepare.
> The main Makefile makes sure that silentoldconfig is ran and therefore
> KERNELRELEASE set for all targets except make *config.

Running make prepare and then re-running a build doesn't rebuild anything
for me.  However, I always build with O=  Also works if I do a make
dtbs too.  So, everything seems to work as expected here.

I think this needs a bit more debugging to see why the whole kernel is
being rebuilt - the kernel build system has methods to tell you why stuff
is being built, which would be a good place to start.

-- 
FTTC broadband for 0.8mile line: currently at 9.5Mbps down 400kbps up
according to speedtest.net.

  reply	other threads:[~2014-11-25 23:51 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-04-01 10:15 [git pull] Devicetree changes for v3.15 Grant Likely
2014-04-01 19:42 ` Paul Bolle
2014-04-01 20:18   ` Rob Herring
     [not found]     ` <CAL_JsqKyLPa9PhNbzda1iPyLjfvQpsUMLR7sGRegYmLsrkY-LQ-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2014-04-01 20:34       ` Paul Bolle
2014-04-01 20:32   ` Grant Likely
     [not found]     ` <20140401203250.0B2A7C408A6-WNowdnHR2B42iJbIjFUEsiwD8/FfD2ys@public.gmane.org>
2014-04-01 20:39       ` Grant Likely
2014-04-01 20:46     ` Paul Bolle
     [not found] ` <CACxGe6vCrkHPL6UNy1p8AO4+z5VFRY6w4_2grQEZQwp_3jJ7Yw-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2014-09-26 12:30   ` Linus Walleij
     [not found]     ` <CACRpkdZoo=P7uTO1rNDD_HUPjfAk26C0=mNYPoZmTV0wcO3V-w-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2014-09-26 14:19       ` Jason Cooper
2014-09-29  8:52         ` Linus Walleij
2014-10-27 15:39           ` Linus Walleij
     [not found]             ` <CACRpkdYmJWy1_vs0tWRA7SvkQnvbXXKqf7pHpH5b5tZ6vR+KJg-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2014-11-02 20:52               ` [PATCH] ARM: kbuild: Fix forced rebuild after 'make dtbs' Jason Cooper
2014-11-25 21:41                 ` Michal Marek
2014-11-25 23:51                   ` Russell King - ARM Linux [this message]
     [not found]                     ` <20141125235150.GH3836-l+eeeJia6m9vn6HldHNs0ANdhmdF6hFW@public.gmane.org>
2014-11-26  0:57                       ` Jason Cooper
2014-11-26 13:57                         ` Linus Walleij
     [not found]                           ` <CACRpkdZJoWbQeuZ4ZXGbQr0+SNG_9ZA+cQkAA0C2F9rnZDYtyQ-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2014-11-26 14:41                             ` Russell King - ARM Linux
     [not found]                               ` <20141126144153.GK3836-l+eeeJia6m9vn6HldHNs0ANdhmdF6hFW@public.gmane.org>
2014-11-28 14:10                                 ` Linus Walleij
     [not found]                                   ` <CACRpkdYwQT3+RLxP_b_kYJoHV4L7sZ7yiU=JZWVq_zHKz0EY_g-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2014-12-01 13:55                                     ` Michal Marek
     [not found]                                       ` <547C7364.8000009-AlSwsSmVLrQ@public.gmane.org>
2014-12-04 11:22                                         ` Grant Likely
2014-12-04 11:24                                           ` Russell King - ARM Linux
2014-11-26  9:39                       ` Michal Marek
     [not found]         ` <20140926141943.GC23926-u4khhh1J0LxI1Ri9qeTfzeTW4wlIGRCZ@public.gmane.org>
2014-09-29 12:49           ` [git pull] Devicetree changes for v3.15 Grant Likely
     [not found]             ` <20140929124922.CBE9FC4150A-WNowdnHR2B42iJbIjFUEsiwD8/FfD2ys@public.gmane.org>
2014-09-29 13:52               ` Jason Cooper

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