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

From: Masami Hiramatsu
Date: Thu Mar 24 2011 - 05:08:49 EST


(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@xxxxxxxxx>
> ---
> 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@xxxxxxxxxxx
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