svn commit: r211738 - head/sys/cddl/contrib/opensolaris/uts/common/dtrace

[Kostik Belousov]

On Tue, Aug 24, 2010 at 12:59:30PM +0100, Rui Paulo wrote:
> 
> On 24 Aug 2010, at 12:48, Kostik Belousov wrote:
> >> +#if defined(sun)
> >> 	for (i = 0; i < NCPU; i++) {
> >> 		mutex_enter(&cpu_core[i].cpuc_pid_lock);
> >> 		mutex_exit(&cpu_core[i].cpuc_pid_lock);
> >> 	}
> >> +#else
> >> +	/* XXX */
> >> +	__asm __volatile("": : :"memory");
> > Indeed XXX. Semantic of acquiring/releasing a mutex, even on Solaris,
> > is much stricter then performing compiler-level memory barrier.
> 
> I don't know what kind of mutexes we have in FreeBSD to mimc this behavior.

I believe that the usual sleepable mutex acquisition provides full barrier
both in Solaris and FreeBSD case. But, I also suspect that there is more
then just membar on current CPU. They use per-cpu mutexes, that is a known
technique to provide biased locking. See
http://blogs.sun.com/dave/resource/Asymmetric-Dekker-Synchronization.txt
for relatively long discussion.
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