From mboxrd@z Thu Jan  1 00:00:00 1970
From: "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH 3/4] x86,asm: Re-work smp_store_mb()
Date: Tue, 12 Jan 2016 14:55:35 -0800
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To: "Michael S. Tsirkin" <mst@redhat.com>, Andy Lutomirski <luto@amacapital.net>
Cc: Davidlohr Bueso <dave@stgolabs.net>, Davidlohr Bueso <dbueso@suse.de>, Peter Zijlstra <peterz@infradead.org>, the arch/x86 maintainers <x86@kernel.org>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, virtualization <virtualization@lists.linux-foundation.org>, Andy Lutomirski <luto@kernel.org>, Thomas Gleixner <tglx@linutronix.de>, "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>, Linus Torvalds <torvalds@linux-foundation.org>, Ingo Molnar <mingo@kernel.org>
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On 01/12/16 14:21, Michael S. Tsirkin wrote:
> 
> OK so I'll have to tweak the test to put something
> on stack to measure the difference: my test tweaks a
> global variable instead.
> I'll try that by tomorrow.
> 
> I couldn't measure any difference between mfence and lock+addl
> except in a micro-benchmark, but hey since we are tweaking this,
> let's do the optimal thing.
> 

Be careful with this: if it only shows up in a microbenchmark, we may
introduce a hard-to-debug regression for no real benefit.

	-hpa