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Re: Once again: test_and_set for CPUs w/o LL/SC

To: "Maciej W. Rozycki" <macro@ds2.pg.gda.pl>
Subject: Re: Once again: test_and_set for CPUs w/o LL/SC
From: Johannes Stezenbach <js@convergence.de>
Date: Thu, 17 Oct 2002 15:11:15 +0200
Cc: "Gleb O. Raiko" <raiko@niisi.msk.ru>, "Kevin D. Kissell" <kevink@mips.com>, linux-mips@linux-mips.org
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On Thu, Oct 17, 2002 at 02:02:35PM +0200, Maciej W. Rozycki wrote:
> On Thu, 17 Oct 2002, Gleb O. Raiko wrote:
> 
> > Implement new sysmips then.
> 
>  I'm not sure if that's a good idea.  Glibc alone uses test_and_set(),
> exchange_and_add(), atomic_add() and compare_and_swap().  Do you want a
> separate syscall for each of these functions?  I think the ll/sc emulation
> may be the best solution after all.  At least it's most flexible and not
> much slower if at all.

Depends on your usage pattern. E.g. we don't run software that uses
atomicity.h (i.e. no C++ code), but heavily use pthread_mutex_lock() etc.
The few uses of atomicity.h internal to glibc don't warrant
any optimizations. So, if the beql-Method would not exist, I would
consider implementing a new sysmips for compare_and_swap().


Regards,
Johannes

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