From mboxrd@z Thu Jan  1 00:00:00 1970
From: pbonzini@redhat.com (Paolo Bonzini)
Date: Wed, 21 Sep 2011 09:20:08 +0200
Subject: [ltt-dev] [URCU PATCH] cmm: provide lightweight rmb/wmb on PPC
In-Reply-To: <20110920165115.GA2955@Krystal>
References: <1316502769-576-1-git-send-email-pbonzini@redhat.com>
	<20110920163125.GA31802@Krystal> <4E78C1C5.2080001@redhat.com>
	<20110920165115.GA2955@Krystal>
Message-ID: <4E799028.1010707@redhat.com>

On 09/20/2011 06:51 PM, Mathieu Desnoyers wrote:
>> >  I think you're right. "eieio;lwsync" is good for rmb, lwsync is good for
>> >  wmb/smp_rmb/smp_wmb.
> I'm not convinced that the "eieio; lwsync" combo would provide the
> ordering we're looking for for cmm_rmb(). AFAIK, eieio orders,
> separately, a) cacheable stores and b) loads and stores to non-cacheable
> memory. AFAIK, lwsync orders cacheable memory ops, but not loads with
> respect to previous stores. So basically, this combo lacks ordering of
> non-cacheable memory accesses with respect to cachable memory accesses.

Yeah, better safe than sorry.

> Why would lwsync be good for cmm_wmb ? Does it order non-cacheable
> writes ?

The manuals say non-cacheable writes are always ordered.

Paolo