linux-kernel - Re: [PATCH v7 4/8] sched: nominate preferred wakeup cpu

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Message-ID: <20081220103602.GC24181@dirshya.in.ibm.com>
Date:	Sat, 20 Dec 2008 16:06:02 +0530
From:	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org, suresh.b.siddha@...el.com,
	venkatesh.pallipadi@...el.com, a.p.zijlstra@...llo.nl,
	mingo@...e.hu, dipankar@...ibm.com, balbir@...ux.vnet.ibm.com,
	vatsa@...ux.vnet.ibm.com, ego@...ibm.com, andi@...stfloor.org,
	davecb@....com, tconnors@...ro.swin.edu.au, maxk@...lcomm.com,
	gregory.haskins@...il.com, pavel@...e.cz,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [PATCH v7 4/8] sched: nominate preferred wakeup cpu

* Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com> [2008-12-20 15:32:28]:

> * Andrew Morton <akpm@...ux-foundation.org> [2008-12-19 20:44:55]:
> 
> > On Sat, 20 Dec 2008 10:06:38 +0530 Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com> wrote:
> > 
> > > > 
> > > > kernel/sched.c: In function 'schedule':
> > > > kernel/sched.c:3679: warning: 'active_balance' may be used uninitialized in this function
> > > > 
> > > > This warning is correct - the code is buggy.
> > > 
> > > Yes this is my code bug.  I did not see the warning in sched.c.  Is
> > > there any build option that I need to pass in order to get -Wall
> > > effect?
> > 
> > That was just with plain old kbuild: `make allmodconfig;make'.
> > 
> > That warning was produced by gcc-4.0.2.  If you're using something more
> > recent then gcc has regressed.
> 
> This is an interesting problem.  I am unable to get that warning in the
> following GCC versions even with a combination of the following
> cmdline options: -Wall -Wextra -Wuninitialized
> 
> gcc version 4.1.2 20070502
> gcc version 4.2.3
> 
> I will look for older gcc and check this out.

I am able to get the above warning in 
gcc version 3.4.6 (Debian 3.4.6-9)
with default kbuild, no additional params.

Did not get the warning in 
gcc version 4.1.3 20080623

Hence there has been some change in GCC that prevented the
uninitialized warning.

--Vaidy
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