linux-kernel - Re: [patch] perf_event_open.2: sample_max

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Date:   Fri, 14 Oct 2016 12:36:10 +0200
From:   "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
To:     Vince Weaver <vincent.weaver@...ne.edu>
Cc:     mtk.manpages@...il.com, linux-man@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Stephane Eranian <eranian@...gle.com>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>
Subject: Re: [patch] perf_event_open.2: sample_max_stack support

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@...ne.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/