linux-kernel - Re: [PATCH 3/3] early_printk: Add simple serialization to early

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Message-Id: <20171004151431.GI3521@linux.vnet.ibm.com>
Date:   Wed, 4 Oct 2017 08:14:31 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Steven Rostedt <rostedt@...dmis.org>, pmladek@...e.com,
        sergey.senozhatsky@...il.com, linux-kernel@...r.kernel.org,
        mingo@...nel.org, tglx@...utronix.de
Subject: Re: [PATCH 3/3] early_printk: Add simple serialization to
 early_vprintk()

On Wed, Oct 04, 2017 at 04:52:47PM +0200, Peter Zijlstra wrote:
> On Wed, Oct 04, 2017 at 10:43:54AM -0400, Steven Rostedt wrote:
> > 
> > My question is not about ordering, but about coherency. Can you have
> > one CPU read a variable that goes into cache, and keep using the cached
> > variable every time the program asks to read it, instead of going out
> > to memory.
> 
> No, not on a coherent system.

What Peter said.  And if you use READ_ONCE() for the reads, than as
far as I know, all the systems that the Linux kernel supports are
coherent systems.

							Thanx, Paul