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

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Date:	Tue, 11 Sep 2012 17:11:52 +0200
From:	Robert Richter <robert.richter@....com>
To:	David Ahern <dsahern@...il.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 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?

> > 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.

Thanks,

-Robert


-- 
Advanced Micro Devices, Inc.
Operating System Research Center

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