Date: Mon, 15 Jan 2001 23:08:14 -0800 (PST) From: John Baldwin <jhb@FreeBSD.org> To: Mark Murray <mark@grondar.za> Cc: cvs-all@FreeBSD.org, cvs-committers@FreeBSD.org, jake@FreeBSD.org Subject: Re: cvs commit: src/sys/i386/include atomic.h Message-ID: <XFMail.010115230814.jhb@FreeBSD.org> In-Reply-To: <200101160615.f0G6FsI31623@gratis.grondar.za>
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On 16-Jan-01 Mark Murray wrote:
>> > This has really helped my SMP stability here locally. The quad xeon has
>> > now
>> > built 4 releases back to back w/o any problems. It never made it through
>> > 2
>> > without locking up before.
>>
>> Well, I've tried to stress test all my SMP test machines today. No lockups
>> so
>> far. The quad xeon did have a problem with a -j 1024 world though (make got
>> a
>> bus error). No console messages though so not sure what that was about. My
>> dual p3-600 had been locking up really bad this past week, but it has had 0
>> problems today with this fix. If other people with SMP can test -current as
>> of
>> this patch and report any lockups, that would be helpful.
>
> Cool! :-)
>
> The other day, we were talking about the random_harvest stuff on IRC,
> and Jake said that he wanted the harvesting to be less expensive. One of the
> things Jake wanted was the mutexes removed. Are mutexes really that
> expensive,
> 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.
> ??
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.
--
John Baldwin <jhb@FreeBSD.org> -- http://www.FreeBSD.org/~jhb/
PGP Key: http://www.baldwin.cx/~john/pgpkey.asc
"Power Users Use the Power to Serve!" - http://www.FreeBSD.org/
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