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

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Date:	Wed, 12 Sep 2012 08:59:10 -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 9:11 AM, Robert Richter wrote:
> On 11.09.12 08:32:55, David Ahern wrote:
>> My guess would be /usr/include/bits/errno.h:
>>
>> /* Linux has no ENOTSUP error code.  */
>> # define ENOTSUP EOPNOTSUPP
>
> Ok, so ENOTSUP is actually the same as EOPNOTSUPP. Since the syscall
> returns a EOPNOTSUPP, I prefer this when checking perf_event_open()
> return codes. ENOTSUP is not used in the kernel. Was there a reason
> for choosing ENOTSUP?

poor memory? laziness? a habit I was not aware I had acquired with using 
ENOTSUP? I mentioned in a prior response I would change it to EOPNOTSUPP 
to be consistent with the 2nd patch -- what the kernel is returning.

>
>>> 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.
>
> Since the error codes are the same, your code should work also on
> bare-metal. Can you test on a host using :ppp? This should trigger the
> same error message as in a vm.

As expected:
$ perf record -e cycles:ppp -a
Error:
'precise' request not supported. Try removing 'p' modifier

Resending patchset in a few minutes.

David
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