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

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

[Andi Kleen]

From: Andi Kleen <ak@linux.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.

Cc: adrian.hunter@intel.com
Signed-off-by: Andi Kleen <ak@linux.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

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

[Arnaldo Carvalho de Melo]

Em Tue, Nov 08, 2016 at 04:11:00PM -0800, Andi Kleen escreveu:
> From: Andi Kleen <ak@linux.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@intel.com
> Signed-off-by: Andi Kleen <ak@linux.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

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

[Arnaldo Carvalho de Melo]

Em Wed, Nov 09, 2016 at 10:14:26AM -0300, Arnaldo Carvalho de Melo escreveu:
> Em Tue, Nov 08, 2016 at 04:11:00PM -0800, Andi Kleen escreveu:
> > From: Andi Kleen <ak@linux.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.

It ended up as:

diff --git a/tools/perf/Documentation/intel-pt.txt b/tools/perf/Documentation/intel-pt.txt
index c6c8318e38a2..4d12db118476 100644
--- a/tools/perf/Documentation/intel-pt.txt
+++ b/tools/perf/Documentation/intel-pt.txt
@@ -546,6 +546,18 @@ mode by using the --per-thread option.
 Privileged vs non-privileged users
 ----------------------------------
 
+The v4.2 kernel introduced support for a context switch metadata event,
+PERF_RECORD_SWITCH, which allows unprivileged users to see when their processes
+are scheduled out and in, just not by whom, which is left for the
+PERF_RECORD_SWITCH_CPU_WIDE, that is only accessible in system wide context,
+which in turn requires CAP_SYS_ADMIN.
+
+Please see the 45ac1403f564 ("perf: Add PERF_RECORD_SWITCH to indicate context
+switches") commit, that introduces these metadata events for further info.
+
+When working with kernels < v4.2, the following considerations must be taken,
+as the sched:sched_switch tracepoints will be used to receive such information:
+
 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.

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

[Adrian Hunter]

On 09/11/16 15:59, Arnaldo Carvalho de Melo wrote:
> Em Wed, Nov 09, 2016 at 10:14:26AM -0300, Arnaldo Carvalho de Melo escreveu:
>> Em Tue, Nov 08, 2016 at 04:11:00PM -0800, Andi Kleen escreveu:
>>> From: Andi Kleen <ak@linux.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.
> 
> It ended up as:
> 
> diff --git a/tools/perf/Documentation/intel-pt.txt b/tools/perf/Documentation/intel-pt.txt
> index c6c8318e38a2..4d12db118476 100644
> --- a/tools/perf/Documentation/intel-pt.txt
> +++ b/tools/perf/Documentation/intel-pt.txt
> @@ -546,6 +546,18 @@ mode by using the --per-thread option.
>  Privileged vs non-privileged users
>  ----------------------------------
>  
> +The v4.2 kernel introduced support for a context switch metadata event,
> +PERF_RECORD_SWITCH, which allows unprivileged users to see when their processes
> +are scheduled out and in, just not by whom, which is left for the
> +PERF_RECORD_SWITCH_CPU_WIDE, that is only accessible in system wide context,
> +which in turn requires CAP_SYS_ADMIN.
> +
> +Please see the 45ac1403f564 ("perf: Add PERF_RECORD_SWITCH to indicate context
> +switches") commit, that introduces these metadata events for further info.
> +
> +When working with kernels < v4.2, the following considerations must be taken,
> +as the sched:sched_switch tracepoints will be used to receive such information:
> +
>  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.

Maybe put that last paragraph about memory limits above the new text.

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

[Arnaldo Carvalho de Melo]

Em Wed, Nov 09, 2016 at 04:01:12PM +0200, Adrian Hunter escreveu:
> On 09/11/16 15:59, Arnaldo Carvalho de Melo wrote:
> > Em Wed, Nov 09, 2016 at 10:14:26AM -0300, Arnaldo Carvalho de Melo escreveu:
> >> Em Tue, Nov 08, 2016 at 04:11:00PM -0800, Andi Kleen escreveu:
> >>> From: Andi Kleen <ak@linux.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.
> > 
> > It ended up as:
> > 
> > diff --git a/tools/perf/Documentation/intel-pt.txt b/tools/perf/Documentation/intel-pt.txt
> > index c6c8318e38a2..4d12db118476 100644
> > --- a/tools/perf/Documentation/intel-pt.txt
> > +++ b/tools/perf/Documentation/intel-pt.txt
> > @@ -546,6 +546,18 @@ mode by using the --per-thread option.
> >  Privileged vs non-privileged users
> >  ----------------------------------
> >  
> > +The v4.2 kernel introduced support for a context switch metadata event,
> > +PERF_RECORD_SWITCH, which allows unprivileged users to see when their processes
> > +are scheduled out and in, just not by whom, which is left for the
> > +PERF_RECORD_SWITCH_CPU_WIDE, that is only accessible in system wide context,
> > +which in turn requires CAP_SYS_ADMIN.
> > +
> > +Please see the 45ac1403f564 ("perf: Add PERF_RECORD_SWITCH to indicate context
> > +switches") commit, that introduces these metadata events for further info.
> > +
> > +When working with kernels < v4.2, the following considerations must be taken,
> > +as the sched:sched_switch tracepoints will be used to receive such information:
> > +
> >  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.
> 
> Maybe put that last paragraph about memory limits above the new text.

Ok, as it is not affected by the new text, thanks.

- Arnaldo

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

[Arnaldo Carvalho de Melo]

Em Wed, Nov 09, 2016 at 04:01:12PM +0200, Adrian Hunter escreveu:
> On 09/11/16 15:59, Arnaldo Carvalho de Melo wrote:
> > Em Wed, Nov 09, 2016 at 10:14:26AM -0300, Arnaldo Carvalho de Melo escreveu:
> > +++ b/tools/perf/Documentation/intel-pt.txt
> > @@ -546,6 +546,18 @@ mode by using the --per-thread option.
> >  Privileged vs non-privileged users
> >  ----------------------------------

> > +The v4.2 kernel introduced support for a context switch metadata event,
> > +PERF_RECORD_SWITCH, which allows unprivileged users to see when their processes
> > +are scheduled out and in, just not by whom, which is left for the
> > +PERF_RECORD_SWITCH_CPU_WIDE, that is only accessible in system wide context,
> > +which in turn requires CAP_SYS_ADMIN.
> > +
> > +Please see the 45ac1403f564 ("perf: Add PERF_RECORD_SWITCH to indicate context
> > +switches") commit, that introduces these metadata events for further info.
> > +
> > +When working with kernels < v4.2, the following considerations must be taken,
> > +as the sched:sched_switch tracepoints will be used to receive such information:
> > +
> >  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.
 
> Maybe put that last paragraph about memory limits above the new text.

Ok, adding your Acked-by, it now stands as, please ack:

commit c955ced680270b95a3de6a2434311befaeaea948
Author: Arnaldo Carvalho de Melo <acme@redhat.com>
Date:   Wed Nov 9 11:04:05 2016 -0300

    perf intel-pt: Update documentation about context switch events
    
    Since the unprivileged sched switch event was added in perf, PT doesn't
    need need perf_event_paranoid=-1 anymore for per cpu decoding.
    
    Add a note stating that that is only needed for kernels < 4.2.
    
    Reported-by: Andi Kleen <ak@linux.intel.com>
    Report-link: http://lkml.kernel.org/r/http://lkml.kernel.org/n/tip-x2ybghpqxxn3zu0m8o7qi42r@git.kernel.org
    Acked-by: Adrian Hunter <adrian.hunter@intel.com>
    Fixes: 45ac1403f564 ("perf: Add PERF_RECORD_SWITCH to indicate context switches")
    Link: http://lkml.kernel.org/n/tip-x2ybghpqxxn3zu0m8o7qi42r@git.kernel.org
    Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

diff --git a/tools/perf/Documentation/intel-pt.txt b/tools/perf/Documentation/intel-pt.txt
index c6c8318e38a2..b0b3007d3c9c 100644
--- a/tools/perf/Documentation/intel-pt.txt
+++ b/tools/perf/Documentation/intel-pt.txt
@@ -550,6 +550,18 @@ 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.
 
+The v4.2 kernel introduced support for a context switch metadata event,
+PERF_RECORD_SWITCH, which allows unprivileged users to see when their processes
+are scheduled out and in, just not by whom, which is left for the
+PERF_RECORD_SWITCH_CPU_WIDE, that is only accessible in system wide context,
+which in turn requires CAP_SYS_ADMIN.
+
+Please see the 45ac1403f564 ("perf: Add PERF_RECORD_SWITCH to indicate context
+switches") commit, that introduces these metadata events for further info.
+
+When working with kernels < v4.2, the following considerations must be taken,
+as the sched:sched_switch tracepoints will be used to receive such information:
+
 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
@@ -564,8 +576,11 @@ sched_switch tracepoint
 -----------------------
 
 The sched_switch tracepoint is used to provide side-band data for Intel PT
-decoding.  sched_switch events are automatically added. e.g. the second event
-shown below
+decoding in kernels where the PERF_RECORD_SWITCH metadata event isn't
+available.
+
+The sched_switch events are automatically added. e.g. the second event shown
+below:
 
 	$ perf record -vv -e intel_pt//u uname
 	------------------------------------------------------------

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

[Adrian Hunter]

On 09/11/16 16:44, Arnaldo Carvalho de Melo wrote:
> Em Wed, Nov 09, 2016 at 04:01:12PM +0200, Adrian Hunter escreveu:
>> On 09/11/16 15:59, Arnaldo Carvalho de Melo wrote:
>>> Em Wed, Nov 09, 2016 at 10:14:26AM -0300, Arnaldo Carvalho de Melo escreveu:
>>> +++ b/tools/perf/Documentation/intel-pt.txt
>>> @@ -546,6 +546,18 @@ mode by using the --per-thread option.
>>>  Privileged vs non-privileged users
>>>  ----------------------------------
> 
>>> +The v4.2 kernel introduced support for a context switch metadata event,
>>> +PERF_RECORD_SWITCH, which allows unprivileged users to see when their processes
>>> +are scheduled out and in, just not by whom, which is left for the
>>> +PERF_RECORD_SWITCH_CPU_WIDE, that is only accessible in system wide context,
>>> +which in turn requires CAP_SYS_ADMIN.
>>> +
>>> +Please see the 45ac1403f564 ("perf: Add PERF_RECORD_SWITCH to indicate context
>>> +switches") commit, that introduces these metadata events for further info.
>>> +
>>> +When working with kernels < v4.2, the following considerations must be taken,
>>> +as the sched:sched_switch tracepoints will be used to receive such information:
>>> +
>>>  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.
>  
>> Maybe put that last paragraph about memory limits above the new text.
> 
> Ok, adding your Acked-by, it now stands as, please ack:

Yes that is good. Thank you!

> 
> commit c955ced680270b95a3de6a2434311befaeaea948
> Author: Arnaldo Carvalho de Melo <acme@redhat.com>
> Date:   Wed Nov 9 11:04:05 2016 -0300
> 
>     perf intel-pt: Update documentation about context switch events
>     
>     Since the unprivileged sched switch event was added in perf, PT doesn't
>     need need perf_event_paranoid=-1 anymore for per cpu decoding.
>     
>     Add a note stating that that is only needed for kernels < 4.2.
>     
>     Reported-by: Andi Kleen <ak@linux.intel.com>
>     Report-link: http://lkml.kernel.org/r/http://lkml.kernel.org/n/tip-x2ybghpqxxn3zu0m8o7qi42r@git.kernel.org
>     Acked-by: Adrian Hunter <adrian.hunter@intel.com>
>     Fixes: 45ac1403f564 ("perf: Add PERF_RECORD_SWITCH to indicate context switches")
>     Link: http://lkml.kernel.org/n/tip-x2ybghpqxxn3zu0m8o7qi42r@git.kernel.org
>     Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
> 
> diff --git a/tools/perf/Documentation/intel-pt.txt b/tools/perf/Documentation/intel-pt.txt
> index c6c8318e38a2..b0b3007d3c9c 100644
> --- a/tools/perf/Documentation/intel-pt.txt
> +++ b/tools/perf/Documentation/intel-pt.txt
> @@ -550,6 +550,18 @@ 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.
>  
> +The v4.2 kernel introduced support for a context switch metadata event,
> +PERF_RECORD_SWITCH, which allows unprivileged users to see when their processes
> +are scheduled out and in, just not by whom, which is left for the
> +PERF_RECORD_SWITCH_CPU_WIDE, that is only accessible in system wide context,
> +which in turn requires CAP_SYS_ADMIN.
> +
> +Please see the 45ac1403f564 ("perf: Add PERF_RECORD_SWITCH to indicate context
> +switches") commit, that introduces these metadata events for further info.
> +
> +When working with kernels < v4.2, the following considerations must be taken,
> +as the sched:sched_switch tracepoints will be used to receive such information:
> +
>  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
> @@ -564,8 +576,11 @@ sched_switch tracepoint
>  -----------------------
>  
>  The sched_switch tracepoint is used to provide side-band data for Intel PT
> -decoding.  sched_switch events are automatically added. e.g. the second event
> -shown below
> +decoding in kernels where the PERF_RECORD_SWITCH metadata event isn't
> +available.
> +
> +The sched_switch events are automatically added. e.g. the second event shown
> +below:
>  
>  	$ perf record -vv -e intel_pt//u uname
>  	------------------------------------------------------------
>