linux-kernel - Re: [PATCH 3/3] perf tool: give user better message if precise is not supported

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Message-ID: <504F4B97.3040701@gmail.com>
Date:	Tue, 11 Sep 2012 08:32:55 -0600
From:	David Ahern <dsahern@...il.com>
To:	Robert Richter <robert.richter@....com>
CC:	acme@...stprotocols.net, linux-kernel@...r.kernel.org,
	peterz@...radead.org, Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH 3/3] perf tool: give user better message if precise is
 not supported

On 9/11/12 8:01 AM, Robert Richter wrote:
>
> Ok, wrong question. Better would have been: Did you run it on a
> non-pebs Intel machine of an non-ibs AMD machine?

Intel: yes. VM for example. All the servers I have now are Nehalem or 
better - ie., with a PEBS.

AMD: no. I do not have any AMD-based servers.

>
>> I do not post patches without testing them. This particular patch was
>> verified in a Virtual Machine (no PEBS) and using :pG modifier.
>>
>> 'egrep -r ENOTSUP tools/perf' shows hits in 3 other files, so I am not
>> the only one using the shortcut. I'll change it in the follow up with
>> better commit messages to make it consistent with patch 2.
>
> For VM this might be valid. Don't know where ENOTSUP comes from. It is
> neither in kernel/events/ nor arch/x86/kernel/cpu/perf.

My guess would be /usr/include/bits/errno.h:

/* Linux has no ENOTSUP error code.  */
# define ENOTSUP EOPNOTSUPP


>
> If you run this bare-metal on older machines which do not support pebs
> or ibs, the syscall returns EOPNOTSUPP. You can trigger the same
> behaviour on newer systems with:
>
>   # perf record -e cycles:ppp -c 2097120 -R -a sleep 1
>
>     Error: sys_perf_event_open() syscall returned with 95 (Operation not supported).  /bin/dmesg may provide additional information.
>   ...
>
> It should work in this case too.

The commit message was a copy and paste from the failure of both :p in a 
VM (PEBS is not supported in a VM). I also ran the bare metal case with 
:pG which per the second patch in this series generates the not 
supported message.

David
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