From: paulmck@linux.vnet.ibm.com (Paul E. McKenney)
Subject: [ltt-dev] [URCU PATCH] cmm: provide lightweight rmb/wmb on PPC
Date: Wed, 21 Sep 2011 16:42:42 -0700 [thread overview]
Message-ID: <20110921234242.GG2394@linux.vnet.ibm.com> (raw)
In-Reply-To: <4E78C1C5.2080001@redhat.com>
On Tue, Sep 20, 2011 at 06:39:33PM +0200, Paolo Bonzini wrote:
> On 09/20/2011 06:31 PM, Mathieu Desnoyers wrote:
> >I don't think lwsync orders non-cacheable memory operations. Therefore,
> >is it the right choice for cmm_rmb/cmm_wmb ?
>
> I think you're right. "eieio;lwsync" is good for rmb, lwsync is good
> for wmb/smp_rmb/smp_wmb.
But eieio;lwsync won't order non-cacheable memory operations against
cacheable memory operations. This means that your MMIO accesses can
slip out of your lock-based critical section, which is a very bad
thing indeed.
For general-purpose use, I strongly recommend full "sync" for mb(),
rmb(), and wmb(). For memory-only use, the developer should not
be using these, but smp_mb(), smp_rmb(), and smp_wmb() instead.
Thanx, Paul
next prev parent reply other threads:[~2011-09-21 23:42 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-09-20 7:12 Paolo Bonzini
2011-09-20 16:31 ` Mathieu Desnoyers
2011-09-20 16:39 ` Paolo Bonzini
2011-09-20 16:51 ` Mathieu Desnoyers
2011-09-21 7:20 ` Paolo Bonzini
2011-09-21 23:43 ` Paul E. McKenney
2011-09-21 23:42 ` Paul E. McKenney [this message]
2011-09-22 8:42 ` [ltt-dev] [PATCH v2] cmm: provide lightweight smp_rmb/smp_wmb " Paolo Bonzini
2011-09-22 9:10 ` Mathieu Desnoyers
2011-09-22 14:49 ` Paul E. McKenney
2011-09-22 14:57 ` Mathieu Desnoyers
2011-09-22 15:26 ` Paul E. McKenney
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