linux-kernel - Re: Getting interrupt every million cache misses

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Date:   Thu, 27 Oct 2016 11:11:04 +0200
From:   Pavel Machek <pavel@....cz>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     acme@...hat.com, kernel list <linux-kernel@...r.kernel.org>,
        mingo@...hat.com, alexander.shishkin@...ux.intel.com
Subject: Re: Getting interrupt every million cache misses

On Thu 2016-10-27 10:28:01, Peter Zijlstra wrote:
> On Wed, Oct 26, 2016 at 10:54:16PM +0200, Pavel Machek wrote:
> > Hi!
> > 
> > I'd like to get an interrupt every million cache misses... to do a
> > printk() or something like that. As far as I can tell, modern hardware
> > should allow me to do that. AFAICT performance events subsystem can do
> > something like that, but I can't figure out where the code is / what I
> > should call.
> > 
> > Can someone help?
> 
> Can you go back one step and explain why you would want this? What use
> is a printk() on every 1e6-th cache miss.
> 
> That is, why doesn't:
> 
>  $ perf record -e cache-misses -c 1000000 -a -- sleep 5
> 
> suffice?

How to work around rowhammer, break my system _and_ make kernel perf
maintainers scream at the same time: (:-) )

I think I got the place now. Let me try...

Thanks,
								Pavel


diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index d31735f..ce83f5e 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -1495,6 +1495,11 @@ perf_event_nmi_handler(unsigned int cmd, struct pt_regs *regs)
 
 	perf_sample_event_took(finish_clock - start_clock);
 
+	/* Here */
+	{
+		udelay(58000);
+	}
+
 	return ret;
 }
 NOKPROBE_SYMBOL(perf_event_nmi_handler);


-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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