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

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Date:	Fri, 14 May 2010 18:56:11 +0800
From:	Lin Ming <ming.m.lin@...el.com>
To:	Cyrill Gorcunov <gorcunov@...il.com>, Ingo Molnar <mingo@...e.hu>
Cc:	Jaswinder Singh Rajput <jaswinderlinux@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Performance Events hangs with Intel P4 system

On Fri, 2010-05-14 at 18:04 +0800, Cyrill Gorcunov wrote:
> On Friday, May 14, 2010, Cyrill Gorcunov <gorcunov@...il.com> wrote:
> > On Friday, May 14, 2010, Jaswinder Singh Rajput
> > <jaswinderlinux@...il.com> wrote:
> >> Hello Cyrill,
> >>
> >> On Fri, May 14, 2010 at 11:53 AM, Cyrill Gorcunov <gorcunov@...il.com> wrote:
> >>> On Friday, May 14, 2010, Cyrill Gorcunov <gorcunov@...il.com> wrote:
> >>>>> Message from syslogd@ht at May 14 09:39:32 ...
> >>>>>  kernel:[  thanks Jaswinder, i'll take a look, meanwhile if you get a chance to
> >>>> test latest -tip/master it would be great
> >>>>
> >>>
> >>> it's found that we have problem in cache events, we're working on
> >>> that, thanks for report!
> >>>
> >>
> >> Great !!
> >>
> >> If you need any help from my side, please let me know. Even though it
> >> is very hot here, I will try my best ;-)
> >>
> >> Thanks,
> >> --
> >> Jaswinder Singh.
> >>
> >
> > Ming is narrowing down the guilty commit. I thought about my last
> > patch related to escr hashing, but it shouldn't bring such effect.
> > Hmm...
> >
> 
> Jaswander, if you manage to bisect it -- this would be just great.

Hi, Jaswinder 

Below patch fixes the regression on my P4 machine.
Would you please have a try it?

Thanks.
---

Subject: [PATCH] x86, perf: P4 PMU -- fix wrong compare

p4_event_bind::cntr is "unsigned char".
But p4_next_cntr has return type of "int".
So the explicit conversion is needed to get the correct result. 

Signed-off-by: Lin Ming <ming.m.lin@...el.com>
---
 arch/x86/kernel/cpu/perf_event_p4.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/perf_event_p4.c b/arch/x86/kernel/cpu/perf_event_p4.c
index cb875b1..9358793 100644
--- a/arch/x86/kernel/cpu/perf_event_p4.c
+++ b/arch/x86/kernel/cpu/perf_event_p4.c
@@ -780,7 +780,7 @@ static int p4_pmu_schedule_events(struct cpu_hw_events *cpuc, int n, int *assign
 		if (unlikely(escr_idx == -1))
 			goto done;
 
-		if (hwc->idx != -1 && !p4_should_swap_ts(hwc->config, cpu)) {
+		if (hwc->idx != (unsigned char)-1 && !p4_should_swap_ts(hwc->config, cpu)) {
 			cntr_idx = hwc->idx;
 			if (assign)
 				assign[i] = hwc->idx;
@@ -788,7 +788,7 @@ static int p4_pmu_schedule_events(struct cpu_hw_events *cpuc, int n, int *assign
 		}
 
 		cntr_idx = p4_next_cntr(thread, used_mask, bind);
-		if (cntr_idx == -1 || test_bit(escr_idx, escr_mask))
+		if (cntr_idx == (unsigned char)-1 || test_bit(escr_idx, escr_mask))
 			goto done;
 
 		p4_pmu_swap_config_ts(hwc, cpu);


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