| Message ID | 1405466172-17055-1-git-send-email-andi@firstfloor.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Hi Andi. On Wed, Jul 16, 2014 at 01:16:11AM +0200, Andi Kleen wrote: > From: Andi Kleen <ak@linux.intel.com> > > This is an alternative approach to lower the overhead of debug info > (as we discussed a few days ago) > > gcc 4.7+ and newer binutils have a new "split debug info" debug info > model where the debug info is only written once into central ".dwo" files. > > This avoids having to copy it around multiple times, from the object > files to the final executable. It also lowers the disk space > requirements. In addition it defaults to compressed debug data. > > More details here: http://gcc.gnu.org/wiki/DebugFission > > This patch adds a new option to enable it. It has to be an option, > because it'll undoubtedly break everyone's debuginfo packaging scheme. > gdb/objdump/etc. all still work, if you have new enough versions. > > I don't see big compile wins (maybe a second or two faster or so), but the > object dirs with debuginfo get significantly smaller. My standard kernel > config (slightly bigger than defconfig) shrinks from 2.9G disk space > to 1.1G objdir (with non reduced debuginfo). I presume if you are IO limited > the compile time difference will be larger. > > Only problem I've seen so far is that it doesn't play well with older > versions of ccache (apparently fixed, see > https://bugzilla.samba.org/show_bug.cgi?id=10005) > > v2: various fixes from Dirk Gouders. Improve commit message slightly. > v3: Fix clean rules and improve Kconfig slightly > Cc: Dirk Gouders <dirk@gouders.net> > Cc: mmarek@suse.cz > Signed-off-by: Andi Kleen <ak@linux.intel.com> > --- > .gitignore | 1 + > Makefile | 5 +++++ > lib/Kconfig.debug | 13 +++++++++++++ > 3 files changed, 19 insertions(+) > > diff --git a/.gitignore b/.gitignore > index f4c0b09..e213b27 100644 > --- a/.gitignore > +++ b/.gitignore > @@ -34,6 +34,7 @@ > *.gcno > modules.builtin > Module.symvers > +*.dwo > > # > # Top-level generic files > diff --git a/Makefile b/Makefile > index 1317563..953659e 100644 > --- a/Makefile > +++ b/Makefile > @@ -683,9 +683,13 @@ endif > endif > > ifdef CONFIG_DEBUG_INFO > +ifdef CONFIG_DEBUG_INFO_SPLIT > +KBUILD_CFLAGS += $(call cc-option, -gsplit-dwarf, -g) > +else > KBUILD_CFLAGS += -g > KBUILD_AFLAGS += -Wa,-gdwarf-2 > endif > +endif Why are as only called with -Wa,-gdwarf-2 in the non-split case? Is this a bug or intentional? If it is intentional then it is not explained. > > ifdef CONFIG_DEBUG_INFO_REDUCED > KBUILD_CFLAGS += $(call cc-option, -femit-struct-debug-baseonly) \ > @@ -1371,6 +1375,7 @@ clean: $(clean-dirs) > @find $(if $(KBUILD_EXTMOD), $(KBUILD_EXTMOD), .) $(RCS_FIND_IGNORE) \ > \( -name '*.[oas]' -o -name '*.ko' -o -name '.*.cmd' \ > -o -name '*.ko.*' \ > + -o -name '*.dwo' \ > -o -name '.*.d' -o -name '.*.tmp' -o -name '*.mod.c' \ > -o -name '*.symtypes' -o -name 'modules.order' \ > -o -name modules.builtin -o -name '.tmp_*.o.*' \ > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug > index 7a638aa..fb07c33 100644 > --- a/lib/Kconfig.debug > +++ b/lib/Kconfig.debug > @@ -143,6 +143,19 @@ config DEBUG_INFO_REDUCED > DEBUG_INFO build and compile times are reduced too. > Only works with newer gcc versions. > > +config DEBUG_INFO_SPLIT > + bool "Produce split debuginfo in .dwo files" Jut nitpicking here - but please be consistent with debuginfo. If it is one or two words. > + depends on DEBUG_INFO > + help > + Generate debug info into separate .dwo files. This can be > + faster for building than including the debug information directly Here the "faster" part is promoted. But in your cover letter you actually highlight the "smaller" case as more significant. Maybe include info on both positive items. > + in the object files and the vmlinux, as it only needs to > + be stored once to disk, not multiple times in object files. > + Requires recent gcc (4.7+) and recent gdb/binutils. > + Any tool that packages or reads debug information would need > + to know about the .dwo files and include them. > + Incompatible with older versions of ccache. Sam -- To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
> Why are as only called with -Wa,-gdwarf-2 in the non-split case? > Is this a bug or intentional? > If it is intentional then it is not explained. Probably was a merging mistake. Will fix. > > + help > > + Generate debug info into separate .dwo files. This can be > > + faster for building than including the debug information directly > Here the "faster" part is promoted. > But in your cover letter you actually highlight the "smaller" case > as more significant. > Maybe include info on both positive items. I currently don't see it significantly faster in my setup, will mention size. It may be in others though. Feel free to test. -Andi -- To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Sun, Jul 20, 2014 at 02:19:01PM -0700, Andi Kleen wrote: > > Why are as only called with -Wa,-gdwarf-2 in the non-split case? > > Is this a bug or intentional? > > If it is intentional then it is not explained. > > Probably was a merging mistake. Will fix. > > > > + help > > > + Generate debug info into separate .dwo files. This can be > > > + faster for building than including the debug information directly > > Here the "faster" part is promoted. > > But in your cover letter you actually highlight the "smaller" case > > as more significant. > > Maybe include info on both positive items. > > I currently don't see it significantly faster in my setup, will > mention size. It may be in others though. Feel free to test. I tried to test this on my setup - it is a Intel Atom with 2 cores. 16 GB RAM, a 7200 RPM stat disk. In other words a low-spec setup. Base config was "make allnoconfig" make KCFLAGS=-g real 3m35.967s user 12m19.270s sys 1m15.082s make KCFLAGS=-gsplit-dwarf real 3m33.366s user 12m11.156s sys 1m17.772s I did like this: echo time make -j4 -s KCFLAGS=-gsplit-dwarf time make -j4 -s KCFLAGS=-gsplit-dwarf echo time make -j4 -s KCFLAGS=-g time make -j4 -s KCFLAGS=-g echo time make -j4 -s KCFLAGS=-gsplit-dwarf time make -j4 -s KCFLAGS=-gsplit-dwarf echo time make -j4 -s KCFLAGS=-g time make -j4 -s KCFLAGS=-g echo time make -j4 -s KCFLAGS=-gsplit-dwarf time make -j4 -s KCFLAGS=-gsplit-dwarf echo time make -j4 -s KCFLAGS=-g time make -j4 -s KCFLAGS=-g The figures are from last run - but the other runs had compareable times. So in short I see a ~3 seconds speedup - out of 210 seconds. Thats less than I anticipated. But a speed-up never the less - which was consistent over all three runs. Sam -- To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
> echo time make -j4 -s KCFLAGS=-gsplit-dwarf > time make -j4 -s KCFLAGS=-gsplit-dwarf > echo time make -j4 -s KCFLAGS=-g > time make -j4 -s KCFLAGS=-g > echo time make -j4 -s KCFLAGS=-gsplit-dwarf > time make -j4 -s KCFLAGS=-gsplit-dwarf > echo time make -j4 -s KCFLAGS=-g > time make -j4 -s KCFLAGS=-g > echo time make -j4 -s KCFLAGS=-gsplit-dwarf > time make -j4 -s KCFLAGS=-gsplit-dwarf > echo time make -j4 -s KCFLAGS=-g > time make -j4 -s KCFLAGS=-g > > The figures are from last run - but the other runs had compareable times. > So in short I see a ~3 seconds speedup - out of 210 seconds. > Thats less than I anticipated. Thanks. How much smaller is it? Just saving disk space is a good thing. -Andi
Andi Kleen <andi@firstfloor.org> writes: >> echo time make -j4 -s KCFLAGS=-gsplit-dwarf >> time make -j4 -s KCFLAGS=-gsplit-dwarf >> echo time make -j4 -s KCFLAGS=-g >> time make -j4 -s KCFLAGS=-g >> echo time make -j4 -s KCFLAGS=-gsplit-dwarf >> time make -j4 -s KCFLAGS=-gsplit-dwarf >> echo time make -j4 -s KCFLAGS=-g >> time make -j4 -s KCFLAGS=-g >> echo time make -j4 -s KCFLAGS=-gsplit-dwarf >> time make -j4 -s KCFLAGS=-gsplit-dwarf >> echo time make -j4 -s KCFLAGS=-g >> time make -j4 -s KCFLAGS=-g >> >> The figures are from last run - but the other runs had compareable times. >> So in short I see a ~3 seconds speedup - out of 210 seconds. >> Thats less than I anticipated. > > Thanks. How much smaller is it? > > Just saving disk space is a good thing. Hi Andi, I applied v3 to rc6+ and did the rudimentary tests that I did with v1, i.e. make menuconfig, make, make clean, git status and have nothing to report. For times an sizes I did tests with my system's .config -- prior to each `make' I did a `make clean': split-debug: # time make -j5 ... real 6m21.819s user 22m48.828s sys 1m1.804s # du -sh . 2.6G . no split-debug: # time make -j5 ... real 6m40.311s user 23m0.648s sys 1m4.592s # du -sh . 4.3G . Dirk -- To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/.gitignore b/.gitignore index f4c0b09..e213b27 100644 --- a/.gitignore +++ b/.gitignore @@ -34,6 +34,7 @@ *.gcno modules.builtin Module.symvers +*.dwo # # Top-level generic files diff --git a/Makefile b/Makefile index 1317563..953659e 100644 --- a/Makefile +++ b/Makefile @@ -683,9 +683,13 @@ endif endif ifdef CONFIG_DEBUG_INFO +ifdef CONFIG_DEBUG_INFO_SPLIT +KBUILD_CFLAGS += $(call cc-option, -gsplit-dwarf, -g) +else KBUILD_CFLAGS += -g KBUILD_AFLAGS += -Wa,-gdwarf-2 endif +endif ifdef CONFIG_DEBUG_INFO_REDUCED KBUILD_CFLAGS += $(call cc-option, -femit-struct-debug-baseonly) \ @@ -1371,6 +1375,7 @@ clean: $(clean-dirs) @find $(if $(KBUILD_EXTMOD), $(KBUILD_EXTMOD), .) $(RCS_FIND_IGNORE) \ \( -name '*.[oas]' -o -name '*.ko' -o -name '.*.cmd' \ -o -name '*.ko.*' \ + -o -name '*.dwo' \ -o -name '.*.d' -o -name '.*.tmp' -o -name '*.mod.c' \ -o -name '*.symtypes' -o -name 'modules.order' \ -o -name modules.builtin -o -name '.tmp_*.o.*' \ diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index 7a638aa..fb07c33 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -143,6 +143,19 @@ config DEBUG_INFO_REDUCED DEBUG_INFO build and compile times are reduced too. Only works with newer gcc versions. +config DEBUG_INFO_SPLIT + bool "Produce split debuginfo in .dwo files" + depends on DEBUG_INFO + help + Generate debug info into separate .dwo files. This can be + faster for building than including the debug information directly + in the object files and the vmlinux, as it only needs to + be stored once to disk, not multiple times in object files. + Requires recent gcc (4.7+) and recent gdb/binutils. + Any tool that packages or reads debug information would need + to know about the .dwo files and include them. + Incompatible with older versions of ccache. + config ENABLE_WARN_DEPRECATED bool "Enable __deprecated logic" default y