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[patch] perf_event_open.2: PERF_RECORD_SWITCH support

Started byVince Weaver <vincent.weaver@maine.edu>
First post2016-10-18 19:30 +0200
Last post2016-10-20 07:50 +0200
Articles 4 — 2 participants

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  [patch] perf_event_open.2: PERF_RECORD_SWITCH support Vince Weaver <vincent.weaver@maine.edu> - 2016-10-18 19:30 +0200
    Re: [patch] perf_event_open.2: PERF_RECORD_SWITCH support "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com> - 2016-10-19 09:10 +0200
      Re: [patch] perf_event_open.2: PERF_RECORD_SWITCH support Vince Weaver <vincent.weaver@maine.edu> - 2016-10-19 17:20 +0200
        Re: [patch] perf_event_open.2: PERF_RECORD_SWITCH support "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com> - 2016-10-20 07:50 +0200

#1503247 — [patch] perf_event_open.2: PERF_RECORD_SWITCH support

FromVince Weaver <vincent.weaver@maine.edu>
Date2016-10-18 19:30 +0200
Subject[patch] perf_event_open.2: PERF_RECORD_SWITCH support
Message-ID<stGn7-4Sx-3@gated-at.bofh.it>
Linux 4.3 introduced two new record types for recording context
switches: PERF_RECORD_SWITCH and PERF_RECORD_SWITCH_CPU_WIDE.

The advantage over the existing tracepoint and software context
switch events is primarily that full switch in/out data can be
gathered even in the face of restrictive perf_event_paranoid
settings.

Signed-off-by: Vince Weaver <vincent.weaver@maine.edu>

diff --git a/man2/perf_event_open.2 b/man2/perf_event_open.2
index 68b99bb..04a0cf5 100644
--- a/man2/perf_event_open.2
+++ b/man2/perf_event_open.2
@@ -243,8 +243,9 @@ struct perf_event_attr {
           comm_exec      :  1,  /* flag comm events that are
                                    due to exec */
           use_clockid    :  1,  /* use clockid for time fields */
+          context_switch :  1,  /* context switch data */
 
-          __reserved_1   : 38;
+          __reserved_1   : 37;
 
     union {
         __u32 wakeup_events;    /* wakeup every n events */
@@ -1112,6 +1113,21 @@ field.
 This can make it easier to correlate perf sample times with
 timestamps generated by other tools.
 .TP
+.IR "context_switch" " (since Linux 4.3)"
+.\" commit 45ac1403f564f411c6a383a2448688ba8dd705a4
+This enables the generation of
+.B PERF_RECORD_SWITCH
+records when a context switch occurs.
+It also enables the generation of
+.B PERF_RECORD_SWITCH_CPU_WIDE
+records when sampling in cpu-wide mode.
+This functionality is in addition to existing tracepoint and
+software events for measuring context switches.
+The advantage of this method is that it will give full
+information event with strict
+.I perf_event_paranoid
+settings.
+.TP
 .IR "wakeup_events" ", " "wakeup_watermark"
 This union sets how many samples
 .RI ( wakeup_events )
@@ -1792,7 +1808,8 @@ Sample happened in guest user code.
 .RE
 
 .RS
-In addition, one of the following bits can be set:
+The following three statuses are generated by
+different record types so they alias to the same bit:
 .TP
 .BR PERF_RECORD_MISC_MMAP_DATA " (since Linux 3.10)"
 .\" commit 2fe85427e3bf65d791700d065132772fc26e4d75
@@ -1807,9 +1824,18 @@ record on kernels more recent than Linux 3.16
 if a process name change was caused by an
 .BR exec (2)
 system call.
-It is an alias for
-.B PERF_RECORD_MISC_MMAP_DATA
-since the two values would not be set in the same record.
+.TP
+.BR PERF_RECORD_MISC_SWITCH_OUT " (since Linux 4.3)"
+.\" commit 45ac1403f564f411c6a383a2448688ba8dd705a4
+When a
+.BR PERF_RECORD_SWITCH " or " PERF_RECORD_SWITCH_CPU_WIDE
+record is generated this bit indicates that the
+context switch is away from the current process
+(instead of in to the current process).
+.RE
+
+.RS
+In addition, the following bits can be set:
 .TP
 .B PERF_RECORD_MISC_EXACT_IP
 This indicates that the content of
@@ -2583,6 +2609,59 @@ struct {
 .I lost
 the number of potentially lost samples.
 .RE
+.TP
+.BR PERF_RECORD_SWITCH " (since Linux 4.3)"
+\" commit 45ac1403f564f411c6a383a2448688ba8dd705a4
+This record indicates a context switch has happened.
+The
+.B PERF_RECORD_MISC_SWITCH_OUT
+bit in the
+.I misc
+field indicates whether it was a context switch into
+or away from the current process.
+
+.in +4n
+.nf
+struct {
+    struct perf_event_header header;
+    struct sample_id sample_id;
+};
+.fi
+.TP
+.BR PERF_RECORD_SWITCH_CPU_WIDE " (since Linux 4.3)"
+\" commit 45ac1403f564f411c6a383a2448688ba8dd705a4
+As with
+.B PERF_RECORD_SWITCH
+this record indicates a context switch has happened,
+but it only occurs when sampling in cpu-wide mode
+and provides additional information on the process
+being switched to/from.
+The
+.B PERF_RECORD_MISC_SWITCH_OUT
+bit in the
+.I misc
+field indicates whether it was a context switch into
+or away from the current process.
+
+.in +4n
+.nf
+struct {
+    struct perf_event_header header;
+    u32 next_prev_pid;
+    u32 next_prev_tid;
+    struct sample_id sample_id;
+};
+.fi
+.RS
+.TP
+.I next_prev_pid
+The process id of the previous (if switching in)
+or next (if switching out) process on the CPU.
+.TP
+.I next_prev_tid
+The thread id of the previous (if switching in)
+or next (if switching out) thread on the CPU.
+.RE
 .RE
 .SS Overflow handling
 Events can be set to notify when a threshold is crossed,

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#1503588

From"Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>
Date2016-10-19 09:10 +0200
Message-ID<stTaF-6ck-9@gated-at.bofh.it>
In reply to#1503247
Hi Vince,

On 10/18/2016 07:22 PM, Vince Weaver wrote:
> 
> Linux 4.3 introduced two new record types for recording context
> switches: PERF_RECORD_SWITCH and PERF_RECORD_SWITCH_CPU_WIDE.
> 
> The advantage over the existing tracepoint and software context
> switch events is primarily that full switch in/out data can be
> gathered even in the face of restrictive perf_event_paranoid
> settings.
> 
> Signed-off-by: Vince Weaver <vincent.weaver@maine.edu>

Thanks! Applied. One query below.

> diff --git a/man2/perf_event_open.2 b/man2/perf_event_open.2
> index 68b99bb..04a0cf5 100644
> --- a/man2/perf_event_open.2
> +++ b/man2/perf_event_open.2
> @@ -243,8 +243,9 @@ struct perf_event_attr {
>            comm_exec      :  1,  /* flag comm events that are
>                                     due to exec */
>            use_clockid    :  1,  /* use clockid for time fields */
> +          context_switch :  1,  /* context switch data */
>  
> -          __reserved_1   : 38;
> +          __reserved_1   : 37;
>  
>      union {
>          __u32 wakeup_events;    /* wakeup every n events */
> @@ -1112,6 +1113,21 @@ field.
>  This can make it easier to correlate perf sample times with
>  timestamps generated by other tools.
>  .TP
> +.IR "context_switch" " (since Linux 4.3)"
> +.\" commit 45ac1403f564f411c6a383a2448688ba8dd705a4
> +This enables the generation of
> +.B PERF_RECORD_SWITCH
> +records when a context switch occurs.
> +It also enables the generation of
> +.B PERF_RECORD_SWITCH_CPU_WIDE
> +records when sampling in cpu-wide mode.
> +This functionality is in addition to existing tracepoint and
> +software events for measuring context switches.
> +The advantage of this method is that it will give full

s/give full/give a full/

ok?

> +information event with strict
> +.I perf_event_paranoid
> +settings.
> +.TP
>  .IR "wakeup_events" ", " "wakeup_watermark"
>  This union sets how many samples
>  .RI ( wakeup_events )
> @@ -1792,7 +1808,8 @@ Sample happened in guest user code.
>  .RE
>  
>  .RS
> -In addition, one of the following bits can be set:
> +The following three statuses are generated by
> +different record types so they alias to the same bit:
>  .TP
>  .BR PERF_RECORD_MISC_MMAP_DATA " (since Linux 3.10)"
>  .\" commit 2fe85427e3bf65d791700d065132772fc26e4d75
> @@ -1807,9 +1824,18 @@ record on kernels more recent than Linux 3.16
>  if a process name change was caused by an
>  .BR exec (2)
>  system call.
> -It is an alias for
> -.B PERF_RECORD_MISC_MMAP_DATA
> -since the two values would not be set in the same record.
> +.TP
> +.BR PERF_RECORD_MISC_SWITCH_OUT " (since Linux 4.3)"
> +.\" commit 45ac1403f564f411c6a383a2448688ba8dd705a4
> +When a
> +.BR PERF_RECORD_SWITCH " or " PERF_RECORD_SWITCH_CPU_WIDE
> +record is generated this bit indicates that the
> +context switch is away from the current process
> +(instead of in to the current process).
> +.RE
> +
> +.RS
> +In addition, the following bits can be set:
>  .TP
>  .B PERF_RECORD_MISC_EXACT_IP
>  This indicates that the content of
> @@ -2583,6 +2609,59 @@ struct {
>  .I lost
>  the number of potentially lost samples.
>  .RE
> +.TP
> +.BR PERF_RECORD_SWITCH " (since Linux 4.3)"
> +\" commit 45ac1403f564f411c6a383a2448688ba8dd705a4
> +This record indicates a context switch has happened.
> +The
> +.B PERF_RECORD_MISC_SWITCH_OUT
> +bit in the
> +.I misc
> +field indicates whether it was a context switch into
> +or away from the current process.
> +
> +.in +4n
> +.nf
> +struct {
> +    struct perf_event_header header;
> +    struct sample_id sample_id;
> +};
> +.fi
> +.TP
> +.BR PERF_RECORD_SWITCH_CPU_WIDE " (since Linux 4.3)"
> +\" commit 45ac1403f564f411c6a383a2448688ba8dd705a4
> +As with
> +.B PERF_RECORD_SWITCH
> +this record indicates a context switch has happened,
> +but it only occurs when sampling in cpu-wide mode
> +and provides additional information on the process
> +being switched to/from.
> +The
> +.B PERF_RECORD_MISC_SWITCH_OUT
> +bit in the
> +.I misc
> +field indicates whether it was a context switch into
> +or away from the current process.
> +
> +.in +4n
> +.nf
> +struct {
> +    struct perf_event_header header;
> +    u32 next_prev_pid;
> +    u32 next_prev_tid;
> +    struct sample_id sample_id;
> +};
> +.fi
> +.RS
> +.TP
> +.I next_prev_pid
> +The process id of the previous (if switching in)
> +or next (if switching out) process on the CPU.
> +.TP
> +.I next_prev_tid
> +The thread id of the previous (if switching in)
> +or next (if switching out) thread on the CPU.
> +.RE
>  .RE
>  .SS Overflow handling
>  Events can be set to notify when a threshold is crossed,
> 

Cheers,

Michael


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/

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#1503870

FromVince Weaver <vincent.weaver@maine.edu>
Date2016-10-19 17:20 +0200
Message-ID<su0OS-308-37@gated-at.bofh.it>
In reply to#1503588
On Wed, 19 Oct 2016, Michael Kerrisk (man-pages) wrote:

> > diff --git a/man2/perf_event_open.2 b/man2/perf_event_open.2
> > index 68b99bb..04a0cf5 100644
> > +.B PERF_RECORD_SWITCH_CPU_WIDE
> > +records when sampling in cpu-wide mode.
> > +This functionality is in addition to existing tracepoint and
> > +software events for measuring context switches.
> > +The advantage of this method is that it will give full
> 
> s/give full/give a full/
> 
> ok?
> 
> > +information event with strict
> > +.I perf_event_paranoid
> > +settings.

What I meant to say was 

"it will give full information *even* with strict perf_event_paranoid 
settings"

Maybe saying something like "despite strict settings" would be better 
wording.

not sure how I missed that typo, apparently my fingers are used to typing 
"event" too much.

Vince

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#1504528

From"Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>
Date2016-10-20 07:50 +0200
Message-ID<sueoO-3mL-17@gated-at.bofh.it>
In reply to#1503870
On 10/19/2016 05:14 PM, Vince Weaver wrote:
> On Wed, 19 Oct 2016, Michael Kerrisk (man-pages) wrote:
> 
>>> diff --git a/man2/perf_event_open.2 b/man2/perf_event_open.2
>>> index 68b99bb..04a0cf5 100644
>>> +.B PERF_RECORD_SWITCH_CPU_WIDE
>>> +records when sampling in cpu-wide mode.
>>> +This functionality is in addition to existing tracepoint and
>>> +software events for measuring context switches.
>>> +The advantage of this method is that it will give full
>>
>> s/give full/give a full/
>>
>> ok?
>>
>>> +information event with strict
>>> +.I perf_event_paranoid
>>> +settings.
> 
> What I meant to say was 
> 
> "it will give full information *even* with strict perf_event_paranoid 
> settings"
> 
> Maybe saying something like "despite strict settings" would be better 
> wording.
> 
> not sure how I missed that typo, apparently my fingers are used to typing 
> "event" too much.

Thanks, Vince. Fixed now.

Cheers,

Michael



-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/

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