linux-kernel - Re: 2.6.28-rc9: oprofile regression

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Date:	Thu, 15 Jan 2009 21:37:00 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Tim Blechmann <tim@...ngt.org>
cc:	Andi Kleen <ak@...ux.intel.com>, oprofile-list@...ts.sf.net,
	linux-kernel@...r.kernel.org,
	Robert Richter <robert.richter@....com>,
	venkatesh.pallipadi@...el.com
Subject: Re: 2.6.28-rc9: oprofile regression

On Thu, 15 Jan 2009, Tim Blechmann wrote:
> On Thu, 2009-01-15 at 09:46 +0100, Thomas Gleixner wrote:
> > Tim,
> > 
> > On Wed, 14 Jan 2009, Tim Blechmann wrote:
> > > this code (line 81/82), changes counter_width from 32 to 40.
> > > 
> > > if (counter_width < eax.split.bit_width)
> > >         counter_width = eax.split.bit_width;
> > > 
> > > however when removing these lines, and thus keeping the value 32 for
> > > counter_width, doesn't change the behavior, only one NMI per cpu.
> > 
> > It would only help, when the reported bit_width would be bogus. We
> > know that you get at least one NMI, so lets look at the results we get
> > there.
> 
> it seems, that ppro_check_ctrs is never called:
> [  982.238639] oprofile: using NMI interrupt.
> 
> hth, tim

Hmm, that confuses the hell out of me. Can you try the patch below,
which restores the original code of writing the counter registers ?

Thanks,

	tglx
---
Subject: x86-oprofile-debug2.patch
From: Thomas Gleixner <tglx@...utronix.de>
Date: Thu, 15 Jan 2009 21:25:55 +0100

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
 arch/x86/oprofile/op_model_ppro.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

Index: linux-2.6/arch/x86/oprofile/op_model_ppro.c
===================================================================
--- linux-2.6.orig/arch/x86/oprofile/op_model_ppro.c
+++ linux-2.6/arch/x86/oprofile/op_model_ppro.c
@@ -101,9 +101,9 @@ static void ppro_setup_ctrs(struct op_ms
 	/* enable active counters */
 	for (i = 0; i < num_counters; ++i) {
 		if ((counter_config[i].enabled) && (CTR_IS_RESERVED(msrs, i))) {
-			reset_value[i] = counter_config[i].count;
+			reset_value[i] = (1ULL << 32) - counter_config[i].count;
 
-			wrmsrl(msrs->counters[i].addr, -reset_value[i]);
+			wrmsr(msrs->counters[i].addr, (u32) reset_value[i], 0);
 
 			CTRL_READ(low, high, msrs, i);
 			CTRL_CLEAR(low);
@@ -132,7 +132,7 @@ static int ppro_check_ctrs(struct pt_reg
 		rdmsrl(msrs->counters[i].addr, val);
 		if (CTR_OVERFLOWED(val)) {
 			oprofile_add_sample(regs, i);
-			wrmsrl(msrs->counters[i].addr, -reset_value[i]);
+			wrmsr(msrs->counters[i].addr, (u32) reset_value[i], 0);
 		}
 	}
 
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