linux-kernel - Re: x86: clean up rwsem type system

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Date:	Sun, 17 Jan 2010 07:05:17 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: x86: clean up rwsem type system


* H. Peter Anvin <hpa@...or.com> wrote:

> On 01/12/2010 06:16 PM, Linus Torvalds wrote:
> > 
> > In case anybody wants to test, the final piece is appended.
> > 
> > Again, note the 32767-thread limit here. So this really does need that 
> > whole "make rwsem_count_t be 64-bit and fix the BIAS values to match" 
> > extension on top of it, but that is conceptually a totally independent 
> > issue.
> > 
> > NOT TESTED! The original patch that this all was based on were tested by 
> > KAMEZAWA Hiroyuki, but maybe I screwed up something when I created the 
> > cleaned-up series, so caveat emptor..
> > 
> > Also note that it _may_ be a good idea to mark some more registers 
> > clobbered on x86-64 in the inline asms instead of saving/restoring them. 
> > They are inline functions, but they are only used in places where there 
> > are not a lot of live registers _anyway_, so doing for example the 
> > clobbers of %r8-%r11 in the asm wouldn't make the fast-path code any 
> > worse, and would make the slow-path code smaller. 
> > 
> 
> Hi Linus,
> 
> I have put these into a separate topic branch in the tip tree, which should 
> get them some test coverage.  I will look at 64-bit counters to support 2^31 
> threads hopefully later this week, unless you prefer to do it yourself.

FYI, -tip testing found that these changes break the UML build:

kernel/built-in.o: In function `__up_read':
/home/mingo/tip/arch/x86/include/asm/rwsem.h:192: undefined reference to `call_rwsem_wake'
kernel/built-in.o: In function `__up_write':
/home/mingo/tip/arch/x86/include/asm/rwsem.h:210: undefined reference to `call_rwsem_wake'
kernel/built-in.o: In function `__downgrade_write':
/home/mingo/tip/arch/x86/include/asm/rwsem.h:228: undefined reference to `call_rwsem_downgrade_wake'
kernel/built-in.o: In function `__down_read':
/home/mingo/tip/arch/x86/include/asm/rwsem.h:112: undefined reference to `call_rwsem_down_read_failed'
kernel/built-in.o: In function `__down_write_nested':
/home/mingo/tip/arch/x86/include/asm/rwsem.h:154: undefined reference to `call_rwsem_down_write_failed'
collect2: ld returned 1 exit status

	Ingo
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