linux-kernel - Re: [PATCH] perf, x86: try to handle unknown nmis with running perfctrs

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Date:	Wed, 11 Aug 2010 11:19:39 +0800
From:	Huang Ying <ying.huang@...el.com>
To:	Don Zickus <dzickus@...hat.com>
Cc:	Robert Richter <robert.richter@....com>,
	Cyrill Gorcunov <gorcunov@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	"Lin, Ming M" <ming.m.lin@...el.com>, Ingo Molnar <mingo@...e.hu>,
	"fweisbec@...il.com" <fweisbec@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Yinghai Lu <yinghai@...nel.org>,
	Andi Kleen <andi@...stfloor.org>
Subject: Re: [PATCH] perf, x86: try to handle unknown nmis with running
 perfctrs

On Wed, 2010-08-11 at 04:48 +0800, Don Zickus wrote:
> > From d2739578199d881ae6a9537c1b96a0efd1cdea43 Mon Sep 17 00:00:00 2001
> > From: Robert Richter <robert.richter@....com>
> > Date: Thu, 5 Aug 2010 16:19:59 +0200
> > Subject: [PATCH] perf, x86: try to handle unknown nmis with running perfctrs
> 
> On top of Robert's patch:
> (compiled tested only because I don't have a fancy button to trigger
> unknown nmis)

You can trigger unknown NMIs via apic->send_IPI_mask(cpu_mask,
NMI_VECTOR).

How about the algorithm as follow:

int perf_event_nmi_handler()
{
	...
	switch (cmd) {
	case DIE_NMIUNKNOWN:
		if (per_cpu(perfctr_prev_handled) > 1
		    && rdtsc() - per_cpu(perfctr_handled_timestamp) < 1000)
			return NOTIFY_STOP;
		else
			return NOTIFY_DONE;
	}
	...
	handled = x86_pmu.handle_irq(regs);
	per_cpu(perfctr_prev_handled) = per_cpu(perfctr_handled);
	per_cpu(perfctr_handled) = handled;
	if (handled) {
		per_cpu(perfctr_handled_timestamp) = rdtsc();
		return NOTIFY_STOP;
	} else
		return NOTIFY_DONE;
}

Best Regards,
Huang Ying


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