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[patch] perf_event_open.2: sample_max_stack support

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  [patch] perf_event_open.2: sample_max_stack support Vince Weaver <vincent.weaver@maine.edu> - 2016-10-13 23:20 +0200
    Re: [patch] perf_event_open.2: sample_max_stack support "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com> - 2016-10-14 12:40 +0200

#1500578 — [patch] perf_event_open.2: sample_max_stack support

Linux 4.8 added a new sample_max_stack parameter, as well as
/proc/sys/kernel/perf_event_max_stack which limits it and a new
EOVERFLOW error return.

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

diff --git a/man2/perf_event_open.2 b/man2/perf_event_open.2
index 3c894cc..edfdb72 100644
--- a/man2/perf_event_open.2
+++ b/man2/perf_event_open.2
@@ -268,7 +268,8 @@ struct perf_event_attr {
     __s32 clockid;              /* clock to use for time fields */
     __u64 sample_regs_intr;     /* regs to dump on samples */
     __u32 aux_watermark;        /* aux bytes before wakeup */
-    __u32 __reserved_2;         /* align to u64 */
+    __u16 sample_max_stack;     /* max frames in callchain */
+    __u16 __reserved_2;         /* align to u64 */
 
 };
 .fi
@@ -1307,6 +1308,15 @@ currently supported.
 This specifies how much data is required to trigger a
 .B PERF_RECORD_AUX
 sample.
+.TP
+.IR "sample_max_stack" " (since Linux 4.8)"
+.\" commit 97c79a38cd454602645f0470ffb444b3b75ce574
+When
+.I sample_type
+includes
+.B PERF_SAMPLE_CALLCHAIN
+this specifies how many stack frames to report when
+generating the callchain.
 .SS Reading results
 Once a
 .BR perf_event_open ()
@@ -2780,6 +2790,14 @@ users to sample at a rate that impacts overall machine performance
 and potentially lock up the machine.
 The default value is
 100000 (samples per second).
+
+.TP
+.I /proc/sys/kernel/perf_event_max_stack
+.\" Introduced in c5dfd78eb79851e278b7973031b9ca363da87a7e
+
+This sets the maximum depth of stack frame entries reported
+when generating a call trace.
+
 .TP
 .I /proc/sys/kernel/perf_event_mlock_kb
 
@@ -3001,6 +3019,15 @@ This includes requesting low-skid events if not supported,
 branch tracing if it is not available, sampling if no PMU
 interrupt is available, and branch stacks for software events.
 .TP
+.BR EOVERFLOW " (since Linux 4.8)"
+.\" 97c79a38cd454602645f0470ffb444b3b75ce574
+Returned if
+.B PERF_SAMPLE_CALLCHAIN
+is requested and
+.I sample_max_stack
+is larger than the maximum specified in
+.IR /proc/sys/kernel/perf_event_max_stack .
+.TP
 .B EPERM
 Returned on many (but not all) architectures when an unsupported
 .IR exclude_hv ", " exclude_idle ", " exclude_user ", or " exclude_kernel

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#1500825

On 10/13/2016 11:16 PM, Vince Weaver wrote:
> 
> Linux 4.8 added a new sample_max_stack parameter, as well as
> /proc/sys/kernel/perf_event_max_stack which limits it and a new
> EOVERFLOW error return.

Thanks, Vince. Applied!

Cheers,

Michael

> Signed-off-by: Vince Weaver <vincent.weaver@maine.edu>
> 
> diff --git a/man2/perf_event_open.2 b/man2/perf_event_open.2
> index 3c894cc..edfdb72 100644
> --- a/man2/perf_event_open.2
> +++ b/man2/perf_event_open.2
> @@ -268,7 +268,8 @@ struct perf_event_attr {
>      __s32 clockid;              /* clock to use for time fields */
>      __u64 sample_regs_intr;     /* regs to dump on samples */
>      __u32 aux_watermark;        /* aux bytes before wakeup */
> -    __u32 __reserved_2;         /* align to u64 */
> +    __u16 sample_max_stack;     /* max frames in callchain */
> +    __u16 __reserved_2;         /* align to u64 */
>  
>  };
>  .fi
> @@ -1307,6 +1308,15 @@ currently supported.
>  This specifies how much data is required to trigger a
>  .B PERF_RECORD_AUX
>  sample.
> +.TP
> +.IR "sample_max_stack" " (since Linux 4.8)"
> +.\" commit 97c79a38cd454602645f0470ffb444b3b75ce574
> +When
> +.I sample_type
> +includes
> +.B PERF_SAMPLE_CALLCHAIN
> +this specifies how many stack frames to report when
> +generating the callchain.
>  .SS Reading results
>  Once a
>  .BR perf_event_open ()
> @@ -2780,6 +2790,14 @@ users to sample at a rate that impacts overall machine performance
>  and potentially lock up the machine.
>  The default value is
>  100000 (samples per second).
> +
> +.TP
> +.I /proc/sys/kernel/perf_event_max_stack
> +.\" Introduced in c5dfd78eb79851e278b7973031b9ca363da87a7e
> +
> +This sets the maximum depth of stack frame entries reported
> +when generating a call trace.
> +
>  .TP
>  .I /proc/sys/kernel/perf_event_mlock_kb
>  
> @@ -3001,6 +3019,15 @@ This includes requesting low-skid events if not supported,
>  branch tracing if it is not available, sampling if no PMU
>  interrupt is available, and branch stacks for software events.
>  .TP
> +.BR EOVERFLOW " (since Linux 4.8)"
> +.\" 97c79a38cd454602645f0470ffb444b3b75ce574
> +Returned if
> +.B PERF_SAMPLE_CALLCHAIN
> +is requested and
> +.I sample_max_stack
> +is larger than the maximum specified in
> +.IR /proc/sys/kernel/perf_event_max_stack .
> +.TP
>  .B EPERM
>  Returned on many (but not all) architectures when an unsupported
>  .IR exclude_hv ", " exclude_idle ", " exclude_user ", or " exclude_kernel
> 


-- 
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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