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Date:   Thu, 21 Jun 2018 22:32:57 +0200 (CEST)
From:   Thomas Gleixner <tglx@linutronix.de>
To:     Fenghua Yu <fenghua.yu@intel.com>
cc:     Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@elte.hu>,
        "H. Peter Anvin" <hpa@linux.intel.com>,
        Ashok Raj <ashok.raj@intel.com>,
        Dave Hansen <dave.hansen@intel.com>,
        Rafael Wysocki <rafael.j.wysocki@intel.com>,
        Tony Luck <tony.luck@intel.com>,
        Alan Cox <alan@linux.intel.com>,
        Ravi V Shankar <ravi.v.shankar@intel.com>,
        Arjan van de Ven <arjan@infradead.org>,
        linux-kernel <linux-kernel@vger.kernel.org>, x86 <x86@kernel.org>
Subject: Re: [RFC PATCH 00/16] x86/split_lock: Enable #AC exception for split
 locked accesses
In-Reply-To: <20180621201851.GC114883@romley-ivt3.sc.intel.com>
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On Thu, 21 Jun 2018, Fenghua Yu wrote:
> On Thu, Jun 21, 2018 at 09:37:38PM +0200, Peter Zijlstra wrote:
> > On Sun, May 27, 2018 at 08:45:49AM -0700, Fenghua Yu wrote:
> > > Currently we can trace split lock event counter for debug purpose. But
> > 
> > How? A while ago I actually tried that, but I could not find a suitable
> > perf event.
> 
> The event name is called sq_misc.split_lock. It's been supported in perf
> already.

So the obvious question is why not simply use that counter and capture the
IP which triggers the event?

I can see that this wont cover the early boot process, but there it's
enough to catch #AC once, yell loudly and then disable the thing. I'm not
seing the value of adding 1000 lines of code with lots of control knobs.

I might be missing something though and am happy to be educated.

Thanks,

	tglx