linux-kernel - Re: [PATCH] x86: Add an explicit barrier() to clflushopt()

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Message-ID: <568EE777.80700@zytor.com>
Date:	Thu, 7 Jan 2016 14:32:23 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Chris Wilson <chris@...is-wilson.co.uk>,
	Andy Lutomirski <luto@...capital.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Ross Zwisler <ross.zwisler@...ux.intel.com>,
	"H . Peter Anvin" <hpa@...ux.intel.com>,
	Borislav Petkov <bp@...en8.de>,
	Brian Gerst <brgerst@...il.com>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Imre Deak <imre.deak@...el.com>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	DRI <dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH] x86: Add an explicit barrier() to clflushopt()

On 01/07/16 14:29, H. Peter Anvin wrote:
> 
> I would be very interested in knowing if replacing the final clflushopt
> with a clflush would resolve your problems (in which case the last mb()
> shouldn't be necessary either.)
> 

Nevermind.  CLFLUSH is not ordered with regards to CLFLUSHOPT to the
same cache line.

Could you add a sync_cpu(); call to the end (can replace the final mb())
and see if that helps your case?

	-hpa