Date: Tue, 24 Aug 2010 15:05:38 +0300 From: Kostik Belousov <kostikbel@gmail.com> To: Rui Paulo <rpaulo@freebsd.org> Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org Subject: Re: svn commit: r211738 - head/sys/cddl/contrib/opensolaris/uts/common/dtrace Message-ID: <20100824120538.GL2396@deviant.kiev.zoral.com.ua> In-Reply-To: <0329C085-13EF-47F1-B8BB-DB7679444FAE@freebsd.org> References: <201008241111.o7OBBwvn074031@svn.freebsd.org> <20100824114818.GJ2396@deviant.kiev.zoral.com.ua> <0329C085-13EF-47F1-B8BB-DB7679444FAE@freebsd.org>
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On Tue, Aug 24, 2010 at 12:59:30PM +0100, Rui Paulo wrote:
>=20
> On 24 Aug 2010, at 12:48, Kostik Belousov wrote:
> >> +#if defined(sun)
> >> for (i =3D 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.
>=20
> I don't know what kind of mutexes we have in FreeBSD to mimc this behavio=
r.
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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