linux-kernel - Re: [PATCH] perf probe: Add fastpath to do lookup by function name

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Date:	Thu, 24 Mar 2011 18:08:35 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Lin Ming <ming.m.lin@...el.com>
Cc:	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] perf probe: Add fastpath to do lookup by function name

(2011/03/25 0:38), Lin Ming wrote:
> The vmlinux file may have thousands of CUs.
> We can lookup function name from .debug_pubnames section
> to avoid the slow loop on CUs.
> 
> Signed-off-by: Lin Ming <ming.m.lin@...el.com>
> ---
>  tools/perf/util/probe-finder.c |   38 ++++++++++++++++++++++++++++++++++++++
>  tools/perf/util/probe-finder.h |    1 +
>  2 files changed, 39 insertions(+), 0 deletions(-)
> 
> diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
> index 194f9e2..b2034c2 100644
> --- a/tools/perf/util/probe-finder.c
> +++ b/tools/perf/util/probe-finder.c
> @@ -1876,6 +1876,30 @@ static int find_line_range_by_func(struct line_finder *lf)
>  	return param.retval;
>  }
>  
> +static int pubname_search_cb(Dwarf *dbg, Dwarf_Global *gl, void *data)
> +{
> +	struct line_finder *lf = data;
> +	struct line_range *lr = lf->lr;
> +
> +	if (dwarf_offdie(dbg, gl->die_offset, &lf->sp_die)) {
> +		if (dwarf_tag(&lf->sp_die) != DW_TAG_subprogram)
> +			return DWARF_CB_OK;
> +
> +		if (die_compare_name(&lf->sp_die, lr->function)) {
> +			if (!dwarf_offdie(dbg, gl->cu_offset, &lf->cu_die))
> +				return DWARF_CB_OK;
> +

Just one comment.
Could you ensure that the decl_file of sp_die matches lr->file (by strtailcmp) here?

Other parts look good to me:)

Thanks!

> +			if (lr->file && !cu_find_realpath(&lf->cu_die, lr->file))
> +				return DWARF_CB_OK;
> +
> +			lf->found = 1;
> +			return DWARF_CB_ABORT;
> +		}
> +	}
> +
> +	return DWARF_CB_OK;
> +}
> +
>  int find_line_range(int fd, struct line_range *lr)
>  {
>  	struct line_finder lf = {.lr = lr, .found = 0};
> @@ -1895,6 +1919,19 @@ int find_line_range(int fd, struct line_range *lr)
>  		return -EBADF;
>  	}
>  
> +	/* Fastpath: lookup by function name from .debug_pubnames section */
> +	if (lr->function) {
> +		struct dwarf_callback_param param = {.data = (void *)&lf, .retval = 0};
> +
> +		dwarf_getpubnames(dbg, pubname_search_cb, &lf, 0);
> +		if (lf.found) {
> +			lf.found = 0;
> +			line_range_search_cb(&lf.sp_die, &param);
> +			if (lf.found)
> +				goto found;
> +		}
> +	}
> +
>  	/* Loop on CUs (Compilation Unit) */
>  	while (!lf.found && ret >= 0) {
>  		if (dwarf_nextcu(dbg, off, &noff, &cuhl, NULL, NULL, NULL) != 0)
> @@ -1923,6 +1960,7 @@ int find_line_range(int fd, struct line_range *lr)
>  		off = noff;
>  	}
>  
> +found:
>  	/* Store comp_dir */
>  	if (lf.found) {
>  		comp_dir = cu_get_comp_dir(&lf.cu_die);
> diff --git a/tools/perf/util/probe-finder.h b/tools/perf/util/probe-finder.h
> index beaefc3..4bc56a4 100644
> --- a/tools/perf/util/probe-finder.h
> +++ b/tools/perf/util/probe-finder.h
> @@ -83,6 +83,7 @@ struct line_finder {
>  	int			lno_s;		/* Start line number */
>  	int			lno_e;		/* End line number */
>  	Dwarf_Die		cu_die;		/* Current CU */
> +	Dwarf_Die		sp_die;
>  	int			found;
>  };
>  


-- 
Masami HIRAMATSU
2nd Dept. Linux Technology Center
Hitachi, Ltd., Systems Development Laboratory
E-mail: masami.hiramatsu.pt@...achi.com
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