linux-kernel - Re: [PATCH] perf tools pt: Remove obsolete paragraph in intel-pt.c

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Date:   Wed, 9 Nov 2016 10:14:26 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Andi Kleen <andi@...stfloor.org>
Cc:     linux-kernel@...r.kernel.org, Andi Kleen <ak@...ux.intel.com>,
        adrian.hunter@...el.com
Subject: Re: [PATCH] perf tools pt: Remove obsolete paragraph in intel-pt.c

Em Tue, Nov 08, 2016 at 04:11:00PM -0800, Andi Kleen escreveu:
> From: Andi Kleen <ak@...ux.intel.com>
> 
> Since the unprivileged sched switch event was added in perf,
> PT doesn't need need perf_event_paranoid=-1 anymore for
> per cpu decoding. So remove the obsolete paragraph in
> the documentation.

Thanks for pointing that out, I'll do something slightly different tho,
pointing out that from kernel X.Y.Z, when the unprivileged
PERF_RECORD_SWITCH metadata event was introduced, this is no longer an
issue, having to be considered only on older kernels.

- Arnaldo
 
> Cc: adrian.hunter@...el.com
> Signed-off-by: Andi Kleen <ak@...ux.intel.com>
> ---
>  tools/perf/Documentation/intel-pt.txt | 10 ----------
>  1 file changed, 10 deletions(-)
> 
> diff --git a/tools/perf/Documentation/intel-pt.txt b/tools/perf/Documentation/intel-pt.txt
> index c6c8318e38a2..c7f817fd3611 100644
> --- a/tools/perf/Documentation/intel-pt.txt
> +++ b/tools/perf/Documentation/intel-pt.txt
> @@ -550,16 +550,6 @@ Unless /proc/sys/kernel/perf_event_paranoid is set to -1, unprivileged users
>  have memory limits imposed upon them.  That affects what buffer sizes they can
>  have as outlined above.
>  
> -Unless /proc/sys/kernel/perf_event_paranoid is set to -1, unprivileged users are
> -not permitted to use tracepoints which means there is insufficient side-band
> -information to decode Intel PT in per-cpu mode, and potentially workload-only
> -mode too if the workload creates new processes.
> -
> -Note also, that to use tracepoints, read-access to debugfs is required.  So if
> -debugfs is not mounted or the user does not have read-access, it will again not
> -be possible to decode Intel PT in per-cpu mode.
> -
> -
>  sched_switch tracepoint
>  -----------------------
>  
> -- 
> 2.5.5