[PATCH] tools/perf: Fix double/triple-build of the feature detectionlogic during 'make install' et al

[Ingo Molnar]

* Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:

> [...]
> 
> Another annoyance during that make was that "make install" seems to want 
> to re-make the thing I just built. That's absolutely horrible, even if 
> I've seen too many broken projects do that. Now, for perf it's not as 
> horrible as for some (because you can do "make install" as a normal 
> user), but it's still a pattern that needs to be called out and needs to 
> die. It's not just that it slows down "make install", it's also that a 
> normal pattern *should* be that you build things as a normal user, and 
> do "make install" as root.

Ok, I think I managed to fix this bug too - see the patch below. Only 
lightly tested, with the most common usecases.

Thanks,

	Ingo

=========================>
Subject: tools/perf: Fix double/triple-build of the feature detection logic during 'make install' et al
From: Ingo Molnar <mingo@xxxxxxxxxx>
Date: Wed Oct 2 06:51:27 CEST 2013

Linus reported the following perf build system bug:

  'Another annoyance during that make was that "make install" seems to
   want to re-make the thing I just built. That's absolutely horrible, [...]'

The targets that got re-built were 'only' the (numerous) feature checks, 
not the whole project - but still it was mighty annoying as the feature 
checks took 9+ seconds even on reasonably fast boxes...

Even with the autodep patches where feature detection is much faster 
double/triple checks waste resources, waste screen real estate and confuse 
users.

There were two sources for these unnecessary re-builds of the feature 
checks:

 - Unnecessary nested invocations of $(MAKE), apparently to be able
   to do conditional compilation dependent on documentation tools
   presence. Use straight dependencies instead, with no nesting.

 - A direct invocation of $(MAKE) to rebuild the PERF-VERSION-FILE.
   This is apparently done to be able to include it into the
   Makefile:

    -include $(OUTPUT)PERF-VERSION-FILE

   but that's entirely pointless for two reasons: 1) the version file
   gets regenerated by the initial build pass anyway, 2) including it
   is futile, given its contents:

    #define PERF_VERSION "3.12.rc3.g8510c7"

   'make' will interpret that as a comment line...

   So just remove this part of the doc-generation logic.

With these things fixed a 'make install' now rebuilds only what is needed.

A repeated 'make install' on an already built tree is super fast now, it 
finishes in under 0.3 seconds:

  #
  #  After the patch:
  #

  $ time make install

  ...

  real    0m0.280s
  user    0m0.162s
  sys     0m0.054s

Prior all the autodep changes and prior this fix, a repeat 'make install' 
took 24.1 seconds (!) on the same system:

  #
  #  Before the patches:
  #

  $ time make install

  ...

  real    0m24.109s
  user    0m21.171s
  sys     0m2.449s

Which almost entirely was caused by fixable build system fat.
We are now literally ~86 times faster.

A fresh rebuild and install now takes just 11.4 seconds:

  #
  #  After the patch:
  #

  $ make clean
  $ time make -j16 install

  ...

  real    0m11.457s
  user    1m43.411s
  sys     0m7.610s

Without the patches it took 27.8 seconds:

  #
  #  Before the patches:
  #

  $ make clean
  $ time make -j16 install

  ...

  real    0m27.801s
  user    1m59.242s
  sys     0m9.749s

So even in the complete rebuild case we are now ~2.5 times faster.

Reported-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Cc: David Ahern <dsahern@xxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 tools/perf/Documentation/Makefile |   17 ++++-------------
 1 file changed, 4 insertions(+), 13 deletions(-)

Index: tip/tools/perf/Documentation/Makefile
===================================================================
--- tip.orig/tools/perf/Documentation/Makefile
+++ tip/tools/perf/Documentation/Makefile
@@ -192,13 +192,14 @@ do-install-man: man
 
 install-man: check-man-tools man
 
-try-install-man:
 ifdef missing_tools
-	$(warning Please install $(missing_tools) to have the man pages installed)
+  DO_INSTALL_MAN = $(warning Please install $(missing_tools) to have the man pages installed)
 else
-	$(MAKE) do-install-man
+  DO_INSTALL_MAN = do-install-man
 endif
 
+try-install-man: $(DO_INSTALL_MAN)
+
 install-info: info
 	$(INSTALL) -d -m 755 $(DESTDIR)$(infodir)
 	$(INSTALL) -m 644 $(OUTPUT)perf.info $(OUTPUT)perfman.info $(DESTDIR)$(infodir)
@@ -216,14 +217,6 @@ install-pdf: pdf
 #install-html: html
 #	'$(SHELL_PATH_SQ)' ./install-webdoc.sh $(DESTDIR)$(htmldir)
 
-ifneq ($(MAKECMDGOALS),clean)
-ifneq ($(MAKECMDGOALS),tags)
-$(OUTPUT)PERF-VERSION-FILE: .FORCE-PERF-VERSION-FILE
-	$(QUIET_SUBDIR0)../ $(QUIET_SUBDIR1) $(OUTPUT)PERF-VERSION-FILE
-
--include $(OUTPUT)PERF-VERSION-FILE
-endif
-endif
 
 #
 # Determine "include::" file references in asciidoc files.
@@ -342,5 +335,3 @@ $(patsubst %.txt,%.html,$(wildcard howto
 
 #quick-install-html:
 #	'$(SHELL_PATH_SQ)' ./install-doc-quick.sh $(HTML_REF) $(DESTDIR)$(htmldir)
-
-.PHONY: .FORCE-PERF-VERSION-FILE
--
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