Date: Thu, 7 Aug 2003 15:22:37 -0400 (EDT) From: Daniel Eischen <eischen@vigrid.com> To: "Portante, Peter" <peter.portante@hp.com> Cc: Marcel Moolenaar <marcel@xcllnt.net> Subject: RE: Atomic swap Message-ID: <Pine.GSO.4.10.10308071517360.29641-100000@pcnet5.pcnet.com> In-Reply-To: <B24FABB430F7C94D942D6386447C93DC0512B561@tayexc17.americas.cpqcorp.net>
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On Thu, 7 Aug 2003, Portante, Peter wrote:
> Dan,
>
> > ----------
> > From: Daniel Eischen
> > Reply To: deischen@freebsd.org
> > Sent: Thursday, August 7, 2003 3:05 PM
> > To: Marcel Moolenaar
> > Cc: Portante, Peter; alpha@freebsd.org; deischen@freebsd.org
> > Subject: Re: Atomic swap
> >
> > On Thu, 7 Aug 2003, Marcel Moolenaar wrote:
> >
> > > static __inline void
> > > atomic_swap_long(volatile long *dst, long val, long *res)
> > > {
> > > __asm ( "1: ldq_l t0,%0\n"
> > > " mov %1,t1\n"
> >
> > If I swap the first 2 instructions:
> >
> > __asm ( "1: mov %1,t1\n"
> > ldq_l t0,%0\n"
> >
> > that eliminates 1 instruction from between the locked
> > instructions. Is there anything wrong with doing that?
> >
> Actually, the processor has a chance to do something while waiting for
> memory, so it does not hurt to have the mov inside the ldq_l/stq_c pair.
I'm just thinking that it could narrow the window in which
you can get a contention, but if the window is the same
regardless of the order of those 2 instructions, then
that's OK.
--
Dan Eischen
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