linux-kernel - Re: [PATCH v5 4/5] x86: use mb() around clflush

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Message-ID: <20160128182541.GW6356@twins.programming.kicks-ass.net>
Date:	Thu, 28 Jan 2016 19:25:41 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Davidlohr Bueso <dave@...olabs.net>,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	the arch/x86 maintainers <x86@...nel.org>,
	Davidlohr Bueso <dbueso@...e.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	virtualization <virtualization@...ts.linux-foundation.org>,
	Borislav Petkov <bp@...en8.de>,
	Mike Galbraith <bitbucket@...ine.de>,
	Ingo Molnar <mingo@...hat.com>,
	Andy Lutomirski <luto@...nel.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Len Brown <len.brown@...el.com>
Subject: Re: [PATCH v5 4/5] x86: use mb() around clflush

On Thu, Jan 28, 2016 at 07:02:51PM +0200, Michael S. Tsirkin wrote:
> commit f8e617f4582995f7c25ef25b4167213120ad122b ("sched/idle/x86:
> Optimize unnecessary mwait_idle() resched IPIs") adds
> memory barriers around clflush, but this seems wrong
> for UP since barrier() has no effect on clflush.
> We really want mfence so switch to mb() instead.
> 
> Cc: Mike Galbraith <bitbucket@...ine.de>
> Signed-off-by: Michael S. Tsirkin <mst@...hat.com>

Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>