Re: Question about PB rule of LKMM

From: Andrea Parri <parri.andrea@gmail.com>
To: Alan Stern <stern@rowland.harvard.edu>
Cc: Kenneth-Lee-2012@foxmail.com, linux-kernel@vger.kernel.org,
	paulmck@kernel.org
Subject: Re: Question about PB rule of LKMM
Date: Wed, 6 Mar 2024 20:24:42 +0100	[thread overview]
Message-ID: <ZejC+lutRuwXQrMz@andrea> (raw)
In-Reply-To: <e05fa6a9-c810-46cb-b033-b91ae7a5c382@rowland.harvard.edu>

> Later on, the file includes this paragraph, which answers the question 
> you were asking:
> 
> ---------------------------------------------------------------------
> The existence of a pb link from E to F implies that E must execute
> before F.  To see why, suppose that F executed first.  Then W would
> have propagated to E's CPU before E executed.  If E was a store, the
> memory subsystem would then be forced to make E come after W in the
> coherence order, contradicting the fact that E ->coe W.  If E was a
> load, the memory subsystem would then be forced to satisfy E's read
> request with the value stored by W or an even later store,
> contradicting the fact that E ->fre W.
> ---------------------------------------------------------------------

TBF, that just explains (not F ->xb E), or I guess that was the origin
of the question.

  Andrea