linux-kernel - Re: perf counters: problem with perf record

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Date:	Mon, 16 Nov 2009 15:25:53 +1000
From:	Simon Kämpflein <s.kaempflein@....de>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Mike Galbraith <efault@....de>, bfweisbec@...il.com,
	linux-kernel@...r.kernel.org
Subject: Re: perf counters: problem with perf record

Ingo Molnar wrote
>> Maybe it's a good idea to add another comment making it clear that the
>> performance counters are not fully working in this case. Or detect this
>> case in "perf-record" and output a message relating to that.
> 
> Ok. Mind sending a patch that changes the message so that it explains it 
> all to you more clearly?

Here's a patch for this:

More accurate error message when "perf record" fails because there is no
APIC support:
---
 tools/perf/builtin-record.c |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index 04f335e..77b21f1 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -303,6 +303,10 @@ try_again:
                printf("\n");
                error("perfcounter syscall returned with %d (%s)\n",
                        fd[nr_cpu][counter], strerror(err));
+
+               if (attr->type == PERF_TYPE_HARDWARE && err == EOPNOTSUPP)
+                        die("No hardware sampling interrupt available.
No APIC? Boot the kernel with the \"lapic\" boot parameter to
force-enable it.\n");
+
                die("No CONFIG_PERF_EVENTS=y kernel support configured?\n");
                exit(-1);
        }
--
1.5.4.3


> 
>>> And does booting with the suggested lapic parameter cure your problems?
>>>
>> Yes, thank you!
> 
> Great.
> 
> You might want to send another patch that allows the .config enabling of 
> that lapic boot parameter. It sucks to carry around boot parameters.
> 

I'm not sure if this is a good idea. Some systems may crash if you
force-enable it:
http://lkml.indiana.edu/hypermail/linux/kernel/0307.3/1635.html

And I'm also not familiar with the kernel internals on that topic ;)

Simon

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