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Date: Sun, 7 Jun 2015 15:11:04 +0200
From: Ingo Molnar <mingo@kernel.org>
To: Arnaldo Carvalho de Melo <acme@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>,
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        Daniel Borkmann <daniel@iogearbox.net>,
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        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
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* Arnaldo Carvalho de Melo <acme@kernel.org> wrote:

> 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.

Yeah, I absolutely love such tooling hints.

Thanks,

	Ingo
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