Date: Tue, 16 Jan 2001 10:06:19 +0200 From: Mark Murray <mark@grondar.za> To: John Baldwin <jhb@FreeBSD.org> Cc: cvs-all@FreeBSD.org, cvs-committers@FreeBSD.org, jake@FreeBSD.org Subject: Atomic ops (Was Re: cvs commit: src/sys/i386/include atomic.h) Message-ID: <200101160806.f0G86GI31855@gratis.grondar.za> In-Reply-To: <XFMail.010115230814.jhb@FreeBSD.org> ; from John Baldwin <jhb@FreeBSD.org> "Mon, 15 Jan 2001 23:08:14 PST." References: <XFMail.010115230814.jhb@FreeBSD.org>
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> > particularly if I just do a
> >
> > if (mutex_try_enter(foo, ...)) {
> > /* Harvest */
> > :
> > mutex_exit(foo, ...);
> > }
> >
> > How much of a difference would it make if I were to use atomic ops like
> >
> > if (atomic_cmpset(foo, 0, 1)) {
> > /* harvest */
> > :
> > foo = 0;
> > }
>
> You would have to use atomic_store_rel() here. And you would have to use
> atomic_cmpset_acq() since you are protecting something.
Right. I'm getting a grasp of whats going on here :-)
> Since you are doing atomic operations with memory barriers either way, I'm not
> sure that the mutex is that much slower, to be perfectly honest.
OK. What I needed to know! I'll figure out an alternative logic. Which
are the "cheaper" atomic ops, and which are the ones to avoid?
M
--
Mark Murray
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