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

To: Johannes Stezenbach <>
Subject: Re: Once again: test_and_set for CPUs w/o LL/SC
From: "Gleb O. Raiko" <>
Date: Thu, 17 Oct 2002 17:32:03 +0400
Cc: "Maciej W. Rozycki" <>, "Kevin D. Kissell" <>,
Organization: NIISI RAN
Original-recipient: rfc822;
References: <> <> <>
Johannes Stezenbach wrote:
> 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().

I didn't look at newer glibc sources (read: greater than 2.0.6), so the
question. Why  is the difference between compare_and_swap and
test_and_set so huge that it eats an exception penalty? ;-)


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