linux-kernel - Re: Performance Events hangs with Intel P4 system

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Date:	Fri, 14 May 2010 22:01:48 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Jaswinder Singh Rajput <jaswinderlinux@...il.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Lin Ming <ming.m.lin@...el.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: Performance Events hangs with Intel P4 system

On Fri, May 14, 2010 at 11:18:52PM +0530, Jaswinder Singh Rajput wrote:
... 
> Earlier I given the command 'ls' which was very small only 601636
> instructions so branches
> and branch-misses came up with <not counted>
> 
> When I given a bigger command 'ls -lR /dev' with 10159428
> instructions, so I get branches and branch-misses count.
> 
> Thanks,
> --
> Jaswinder Singh.
> 

Jaswinder, could you give this patch a shot so that I will be
able to put your tested-by tag and send it upstream? (it's slightly
tuned from previous but should be same on bin level). This GP
issue need to be fixed before any other things.

	-- Cyrill
---
 arch/x86/kernel/cpu/perf_event_p4.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

Index: linux-2.6.git/arch/x86/kernel/cpu/perf_event_p4.c
=====================================================================
--- linux-2.6.git.orig/arch/x86/kernel/cpu/perf_event_p4.c
+++ linux-2.6.git/arch/x86/kernel/cpu/perf_event_p4.c
@@ -18,7 +18,7 @@
 struct p4_event_bind {
 	unsigned int opcode;			/* Event code and ESCR selector */
 	unsigned int escr_msr[2];		/* ESCR MSR for this event */
-	unsigned char cntr[2][P4_CNTR_LIMIT];	/* counter index (offset), -1 on abscence */
+	char cntr[2][P4_CNTR_LIMIT];		/* counter index (offset), -1 on abscence */
 };
 
 struct p4_cache_event_bind {
@@ -747,11 +747,11 @@ static int p4_get_escr_idx(unsigned int 
 static int p4_next_cntr(int thread, unsigned long *used_mask,
 			struct p4_event_bind *bind)
 {
-	int i = 0, j;
+	int i, j;
 
 	for (i = 0; i < P4_CNTR_LIMIT; i++) {
-		j = bind->cntr[thread][i++];
-		if (j == -1 || !test_bit(j, used_mask))
+		j = bind->cntr[thread][i];
+		if (j != -1 && !test_bit(j, used_mask))
 			return j;
 	}
 
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