Re: [PATCH v2 4/4] perf-top: add --max-stack option to limitcallchain stack scan

[Davidlohr Bueso]

On Fri, 2013-10-18 at 10:38 -0400, Waiman Long wrote:
> When the callgraph function is enabled (-G), it may take a long time to
> scan all the stack data and merge them accordingly.
> 
> This patch adds a new --max-stack option to perf-top to limit the depth
> of callchain stack data to look at to reduce the time it takes for
> perf-top to finish its processing. It reduces the amount of information
> provided to the user in exchange for faster speed.
> 
> Signed-off-by: Waiman Long <Waiman.Long@xxxxxx>

Tested-by: Davidlohr Bueso <davidlohr@xxxxxx>

> ---
>  tools/perf/Documentation/perf-top.txt |    8 ++++++++
>  tools/perf/builtin-top.c              |    8 ++++++--
>  tools/perf/util/top.h                 |    1 +
>  3 files changed, 15 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/perf/Documentation/perf-top.txt b/tools/perf/Documentation/perf-top.txt
> index 58d6598..3fd911c 100644
> --- a/tools/perf/Documentation/perf-top.txt
> +++ b/tools/perf/Documentation/perf-top.txt
> @@ -155,6 +155,14 @@ Default is to monitor all CPUS.
>  
>  	Default: fractal,0.5,callee.
>  
> +--max-stack::
> +	Set the stack depth limit when parsing the callchain, anything
> +	beyond the specified depth will be ignored. This is a trade-off
> +	between information loss and faster processing especially for
> +	workloads that can have a very long callchain stack.
> +
> +	Default: 127
> +
>  --ignore-callees=<regex>::
>          Ignore callees of the function(s) matching the given regex.
>          This has the effect of collecting the callers of each such
> diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c
> index 2725aca..14902b0 100644
> --- a/tools/perf/builtin-top.c
> +++ b/tools/perf/builtin-top.c
> @@ -772,7 +772,7 @@ static void perf_event__process_sample(struct perf_tool *tool,
>  			err = machine__resolve_callchain(machine, evsel,
>  							 al.thread, sample,
>  							 &parent, &al,
> -							 PERF_MAX_STACK_DEPTH);
> +							 top->max_stack);
>  			if (err)
>  				return;
>  		}
> @@ -1052,10 +1052,11 @@ int cmd_top(int argc, const char **argv, const char *prefix __maybe_unused)
>  			.user_freq	= UINT_MAX,
>  			.user_interval	= ULLONG_MAX,
>  			.freq		= 4000, /* 4 KHz */
> -			.target		     = {
> +			.target		= {
>  				.uses_mmap   = true,
>  			},
>  		},
> +		.max_stack	     = PERF_MAX_STACK_DEPTH,
>  		.sym_pcnt_filter     = 5,
>  	};
>  	struct perf_record_opts *opts = &top.record_opts;
> @@ -1110,6 +1111,9 @@ int cmd_top(int argc, const char **argv, const char *prefix __maybe_unused)
>  	OPT_CALLBACK_DEFAULT('G', "call-graph", &top.record_opts,
>  			     "mode[,dump_size]", record_callchain_help,
>  			     &parse_callchain_opt, "fp"),
> +	OPT_INTEGER(0, "max-stack", &top.max_stack,
> +		    "Set the maximum stack depth when parsing the callchain. "
> +		    "Default: " __stringify(PERF_MAX_STACK_DEPTH)),
>  	OPT_CALLBACK(0, "ignore-callees", NULL, "regex",
>  		   "ignore callees of these functions in call graphs",
>  		   report_parse_ignore_callees_opt),
> diff --git a/tools/perf/util/top.h b/tools/perf/util/top.h
> index b554ffc..88cfeaf 100644
> --- a/tools/perf/util/top.h
> +++ b/tools/perf/util/top.h
> @@ -24,6 +24,7 @@ struct perf_top {
>  	u64		   exact_samples;
>  	u64		   guest_us_samples, guest_kernel_samples;
>  	int		   print_entries, count_filter, delay_secs;
> +	int		   max_stack;
>  	bool		   hide_kernel_symbols, hide_user_symbols, zero;
>  	bool		   use_tui, use_stdio;
>  	bool		   kptr_restrict_warned;


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