Re: [PATCH v4] modpost: check for static EXPORT_SYMBOL* functions

Masahiro Yamada
2019-07-31T08:55:23Z

Hi.

On Wed, Jul 31, 2019 at 3:12 AM Denis Efremov <efremov@linux.com> wrote:
>
> This patch adds a check to warn about static EXPORT_SYMBOL* functions
> during the modpost. In most of the cases, a static symbol marked for
> exporting is an odd combination that should be fixed either by deleting
> the exporting mark or by removing the static attribute and adding the
> appropriate declaration to headers.
>
> This check could help to detect the following problems:
> 1. 550113d4e9f5 ("i2c: add newly exported functions to the header, too")
> 2. 54638c6eaf44 ("net: phy: make exported variables non-static")
> 3. 98ef2046f28b ("mm: remove the exporting of totalram_pages")
> 4. 73df167c819e ("s390/zcrypt: remove the exporting of ap_query_configuration")
> 5. a57caf8c527f ("sunrpc/cache: remove the exporting of cache_seq_next")
> 6. e4e4730698c9 ("crypto: skcipher - remove the exporting of skcipher_walk_next")
> 7. 14b4c48bb1ce ("gve: Remove the exporting of gve_probe")
> 8. 9b79ee9773a8 ("scsi: libsas: remove the exporting of sas_wait_eh")
> 9. ...
>
> Build time impact, allmodconfig, Dell XPS 15 9570 (measurements 3x):
> $ make mrproper; make allmodconfig; time make -j12; \
> git checkout HEAD~1; \
> make mrproper; make allmodconfig; time make -j12
> 1.
> (with patch) 17635,94s user 1895,54s system 1085% cpu 29:59,22 total
> (w/o patch) 17275,42s user 1803,87s system 1112% cpu 28:35,66 total
> 2.
> (with patch) 17369,51s user 1763,28s system 1111% cpu 28:41,47 total
> (w/o patch) 16880,50s user 1670,93s system 1113% cpu 27:46,56 total
> 3.
> (with patch) 17937,88s user 1842,53s system 1109% cpu 29:42,26 total
> (w/o patch) 17267,55s user 1725,09s system 1111% cpu 28:28,17 total
>
> The check adds less than a minute to a usual build.

I am not convinced with this analysis.

Since commit b7dca6dd1e591ad19,
scripts/mod/modpost is only invoked from scripts/Makefile.modpost.

So, it is much easier to to measure the elapsed time
of modpost directly.

I applied your patch on top next-20190731,
and the following:

diff --git a/scripts/Makefile.modpost b/scripts/Makefile.modpost
index 92ed02d7cd5e..e0db1a626e50 100644
--- a/scripts/Makefile.modpost
+++ b/scripts/Makefile.modpost
@@ -98,7 +98,7 @@ MODPOST += $(subst -i,-n,$(filter -i,$(MAKEFLAGS)))
-s -T - $(wildcard vmlinux)

# We can go over command line length here, so be careful.
quiet_cmd_modpost = MODPOST $(words $(modules)) modules
- cmd_modpost = sed 's/ko$$/o/' $(modorder) | $(MODPOST)
+ cmd_modpost = sed 's/ko$$/o/' $(modorder) | time -o
modpost-time.txt $(MODPOST)

PHONY += modules-modpost
modules-modpost:

The difference is less than 1 sec (not 1 min!) even for allmodconfig.
So, the performance regression is almost unnoticeable level.

--
Best Regards
Masahiro Yamada