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Date: Fri, 5 Jun 2015 11:06:48 -0300
From: Arnaldo Carvalho de Melo <acme@kernel.org>
To: Ingo Molnar <mingo@kernel.org>
Cc: "Wangnan (F)" <wangnan0@huawei.com>, Alexei Starovoitov <ast@plumgrid.com>,
        pi3orama <pi3orama@163.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Adrian Hunter <adrian.hunter@intel.com>,
        Brendan Gregg <brendan.d.gregg@gmail.com>,
        Daniel Borkmann <daniel@iogearbox.net>,
        David Ahern <dsahern@gmail.com>, He Kuang <hekuang@huawei.com>,
        Jiri Olsa <jolsa@redhat.com>, Kaixu Xia <xiakaixu@huawei.com>,
        Madhavan Srinivasan <maddy@linux.vnet.ibm.com>,
        Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Namhyung Kim <namhyung@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>,
        Zefan Li <lizefan@huawei.com>,
        Alexei Starovoitov <alexei.starovoitov@gmail.com>
Subject: Re: [GIT PULL 0/6] perf/core improvements and fixes
Message-ID: <20150605140648.GJ32707@kernel.org>
References: <556FEB32.8040909@huawei.com>
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 <20150604124033.GA10580@gmail.com>
 <0108CD89-BFFA-4A68-90AE-A34597777641@163.com>
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Em Fri, Jun 05, 2015 at 02:05:50PM +0200, Ingo Molnar escreveu:
> * Wangnan (F) <wangnan0@huawei.com> wrote:
<SNIP>
> > One problem I can find is that, the wrapper will make perf depend on llvm. I 
> > don't think the compiler will be deployed in production environments... And 
> > also, the embedded case...
 
> What dependencies are there?
 
> On the usage side there should be very few outright dependencies: if the llvm 
> binary is not available, or doesn't support what you need, or there's no runtime 
> environment you can use to build the bytecode, you should display an informative 
> error message so that the user knows what is missing and how to install it.

Right, something like:

[acme@zoo ~]$ perf trace -e nanosleep usleep 1
Error:	No permissions to read /sys/kernel/debug/tracing/events/raw_syscalls/sys_(enter|exit)
Hint:	Try 'sudo mount -o remount,mode=755 /sys/kernel/debug'
[acme@zoo ~]$ sudo mount -o remount,mode=755 /sys/kernel/debug
[sudo] password for acme: 
[acme@zoo ~]$ perf trace -e nanosleep usleep 1
     0.565 ( 0.060 ms): usleep/17648 nanosleep(rqtp: 0x7fff22baebf0) = 0
[acme@zoo ~]$ perf trace --all-cpus
Error:	Operation not permitted.
Hint:	Check /proc/sys/kernel/perf_event_paranoid setting.
Hint:	For system wide tracing it needs to be set to -1.
Hint:	Try: 'sudo sh -c "echo -1 > /proc/sys/kernel/perf_event_paranoid"'
Hint:	The current value is 1.
[acme@zoo ~]$ 
[acme@zoo ~]$ trace -a -e poll usleep 1
[acme@zoo ~]$ trace -a -e poll usleep 1
 0.041 ( 0.000 ms): firefox/1458  ... [continued]: poll()) = 1
 0.267 ( 0.003 ms): firefox/1458 poll(ufds: 0x7f43d6ea1340, nfds: 5) = 0 Timeout
 0.275 ( 0.001 ms): firefox/1458 poll(ufds: 0x7f43d6ea1340, nfds: 5) = 0 Timeout
 0.283 ( 0.001 ms): firefox/1458 poll(ufds: 0x7f43d6ea1340, nfds: 5) = 0 Timeout
 0.979 ( 0.000 ms): gnome-terminal/2572  ... [continued]: poll()) = 1
 1.056 ( 0.768 ms): firefox/1458 poll(ufds: 0x7f43d6ea1340, nfds: 5, timeout_msecs: 4294967295) ...
 1.065 ( 0.009 ms): gnome-terminal/2572 poll(ufds: 0x1934250, nfds: 23, timeout_msecs: 10) = 1
 1.087 ( 0.007 ms): gnome-terminal/2572 poll(ufds: 0x1934250, nfds: 23, timeout_msecs: 10) = 2
 1.132 ( 0.007 ms): gnome-terminal/2572 poll(ufds: 0x1934250, nfds: 23, timeout_msecs: 10) = 1
 1.161 ( 0.013 ms): gnome-terminal/2572 poll(ufds: 0x1934250, nfds: 23, timeout_msecs: 10) = 1
[acme@zoo ~]$

I.e. Explain the mistake and provide a hint to solve it, as close to the actual
commands needed to perform such corrective/enabling action as possible.

- Arnaldo