Re: [PATCH 3/3] perf tool: give user better message if precise isnot supported

From: David Ahern
Date: Wed Sep 12 2012 - 10:59:10 EST

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. */

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
'precise' request not supported. Try removing 'p' modifier

Resending patchset in a few minutes.

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