Re: [RFC PATCH 00/16] x86/split_lock: Enable #AC exception for split locked accesses

[Thomas Gleixner]

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