| Message ID | 23e0ba7863d51ab629498762a97d477645aeafea.1653123744.git.christophe.jaillet@wanadoo.fr (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [RFC] kbuild: Add an option to enable -O1 and speed-up compilation time | expand |
(+CC: Arnd, Changbin Du) If -O1 support does not require additional effort, I have no objection to this patch. (but I do not have enough insight about the compiler's inlining heuristic) BTW, when we attempted to add the -Og support, we fixed various parts, and Linus rejected it. https://lore.kernel.org/linux-kbuild/CAK7LNARQggM3aKEPRKJqa4tunFAfmfErMZuS-rrnRv6UB1VpPQ@mail.gmail.com/ On Sat, May 21, 2022 at 6:04 PM Christophe JAILLET <christophe.jaillet@wanadoo.fr> wrote: > > Add a new compilation option which speeds-up compilation time. > This can be useful when using static checker such as smatch or build-bots. > In such cases, the speed and quality of the generated code is not > important. > > Using -O0 would be even better, but unfortunately, building fails with > this option. > > Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr> > --- > Makefile | 5 ++++- > init/Kconfig | 8 ++++++++ > 2 files changed, 12 insertions(+), 1 deletion(-) > > diff --git a/Makefile b/Makefile > index 1f8bef92868f..14467386f947 100644 > --- a/Makefile > +++ b/Makefile > @@ -817,7 +817,10 @@ KBUILD_CFLAGS += $(call cc-disable-warning, format-truncation) > KBUILD_CFLAGS += $(call cc-disable-warning, format-overflow) > KBUILD_CFLAGS += $(call cc-disable-warning, address-of-packed-member) > > -ifdef CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE > +ifdef CONFIG_CC_OPTIMIZE_FOR_COMPILATION_SPEED > +KBUILD_CFLAGS += -O1 > +KBUILD_RUSTFLAGS_OPT_LEVEL_MAP := 1 > +else ifdef CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE > KBUILD_CFLAGS += -O2 > KBUILD_RUSTFLAGS_OPT_LEVEL_MAP := 2 > else ifdef CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3 > diff --git a/init/Kconfig b/init/Kconfig > index a96776a9b080..3177a1830c9a 100644 > --- a/init/Kconfig > +++ b/init/Kconfig > @@ -1384,6 +1384,14 @@ choice > prompt "Compiler optimization level" > default CC_OPTIMIZE_FOR_PERFORMANCE > > +config CC_OPTIMIZE_FOR_COMPILATION_SPEED > + bool "Optimize for compilation speed (-O1)" > + help > + This option can be useful when running a static checker such as smatch > + or a build-bot. > + Compilation time is slighly faster than -O2 and it requires less > + memory. > + > config CC_OPTIMIZE_FOR_PERFORMANCE > bool "Optimize for performance (-O2)" > help > -- > 2.34.1 >
On Sun, May 22, 2022 at 12:38:17AM +0900, Masahiro Yamada wrote: > (+CC: Arnd, Changbin Du) > > > If -O1 support does not require additional effort, > I have no objection to this patch. > > (but I do not have enough insight about > the compiler's inlining heuristic) > > > > BTW, when we attempted to add the -Og support, > we fixed various parts, and Linus rejected it. > > https://lore.kernel.org/linux-kbuild/CAK7LNARQggM3aKEPRKJqa4tunFAfmfErMZuS-rrnRv6UB1VpPQ@mail.gmail.com/ > > > > > > > I am afraid that '-O1' has the same situation with '-Og'. As described in GCC mannual: Like -O0, -Og completely disables a number of optimization passes so that individual options controlling them have no effect. Otherwise -Og enables all -O1 optimization flags except for those that may interfere with debugging: -fbranch-count-reg -fdelayed-branch -fdse -fif-conversion -fif-conversion2 -finline-functions-called-once -fmove-loop-invariants -fmove-loop-stores -fssa-phiopt -ftree-bit-ccp -ftree-dse -ftree-pta -ftree-sra > On Sat, May 21, 2022 at 6:04 PM Christophe JAILLET > <christophe.jaillet@wanadoo.fr> wrote: > > > > Add a new compilation option which speeds-up compilation time. > > This can be useful when using static checker such as smatch or build-bots. > > In such cases, the speed and quality of the generated code is not > > important. > > > > Using -O0 would be even better, but unfortunately, building fails with > > this option. > > > > Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr> > > --- > > Makefile | 5 ++++- > > init/Kconfig | 8 ++++++++ > > 2 files changed, 12 insertions(+), 1 deletion(-) > > > > diff --git a/Makefile b/Makefile > > index 1f8bef92868f..14467386f947 100644 > > --- a/Makefile > > +++ b/Makefile > > @@ -817,7 +817,10 @@ KBUILD_CFLAGS += $(call cc-disable-warning, format-truncation) > > KBUILD_CFLAGS += $(call cc-disable-warning, format-overflow) > > KBUILD_CFLAGS += $(call cc-disable-warning, address-of-packed-member) > > > > -ifdef CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE > > +ifdef CONFIG_CC_OPTIMIZE_FOR_COMPILATION_SPEED > > +KBUILD_CFLAGS += -O1 > > +KBUILD_RUSTFLAGS_OPT_LEVEL_MAP := 1 > > +else ifdef CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE > > KBUILD_CFLAGS += -O2 > > KBUILD_RUSTFLAGS_OPT_LEVEL_MAP := 2 > > else ifdef CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3 > > diff --git a/init/Kconfig b/init/Kconfig > > index a96776a9b080..3177a1830c9a 100644 > > --- a/init/Kconfig > > +++ b/init/Kconfig > > @@ -1384,6 +1384,14 @@ choice > > prompt "Compiler optimization level" > > default CC_OPTIMIZE_FOR_PERFORMANCE > > > > +config CC_OPTIMIZE_FOR_COMPILATION_SPEED > > + bool "Optimize for compilation speed (-O1)" > > + help > > + This option can be useful when running a static checker such as smatch > > + or a build-bot. > > + Compilation time is slighly faster than -O2 and it requires less > > + memory. > > + > > config CC_OPTIMIZE_FOR_PERFORMANCE > > bool "Optimize for performance (-O2)" > > help > > -- > > 2.34.1 > > > > > -- > Best Regards > Masahiro Yamada
On Mon, May 23, 2022 at 2:34 PM Changbin Du <changbin.du@gmail.com> wrote: > On Sun, May 22, 2022 at 12:38:17AM +0900, Masahiro Yamada wrote: > > (+CC: Arnd, Changbin Du) > > > > > > If -O1 support does not require additional effort, > > I have no objection to this patch. > > > > (but I do not have enough insight about > > the compiler's inlining heuristic) > > > > > > > > BTW, when we attempted to add the -Og support, > > we fixed various parts, and Linus rejected it. > > > > https://lore.kernel.org/linux-kbuild/CAK7LNARQggM3aKEPRKJqa4tunFAfmfErMZuS-rrnRv6UB1VpPQ@mail.gmail.com/ > > > > > > > > > > > > > > > I am afraid that '-O1' has the same situation with '-Og'. As described in GCC > mannual: > > Like -O0, -Og completely disables a number of optimization passes so that > individual options controlling them have no effect. Otherwise -Og enables all > -O1 optimization flags except for those that may interfere with debugging: > -fbranch-count-reg -fdelayed-branch > -fdse -fif-conversion -fif-conversion2 > -finline-functions-called-once > -fmove-loop-invariants -fmove-loop-stores -fssa-phiopt > -ftree-bit-ccp -ftree-dse -ftree-pta -ftree-sra Correct, I'm fairly sure this never worked. It may be possible to narrow down the individual optimization flags to have something that works inbetween -O1 and -O2, but that requires a lot of testing work, and it is questionable whether there are any practical upsides. Note that we already disable some optimizations for certain configurations, e.g. CONFIG_READABLE_ASM, CONFIG_FRAME_POINTER or CONFIG_DEBUG_SECTION_MISMATCH. The gcc manual suggests listing all optimization flags with $ gcc -c -Q -O1 --help=optimizers > O1-opts $ gcc -c -Q -O2 --help=optimizers > O2-opts $ diff -u O1-opts O2-opts If the goal is to speed up compilation, there may be value in trying which of the various options make the most difference here and still produce a working kernel when disabled. I know we need the inlining to happen or things go badly wrong, but I don't know if e.g. -fno-expensive-optimizations would work. Arnd
On Sat, May 21, 2022 at 2:04 AM Christophe JAILLET <christophe.jaillet@wanadoo.fr> wrote: > > Add a new compilation option which speeds-up compilation time. > This can be useful when using static checker such as smatch or build-bots. > In such cases, the speed and quality of the generated code is not > important. > > Using -O0 would be even better, but unfortunately, building fails with > this option. Which is a tragedy. As with the Rust series, I'm not a fan of this (or CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3): https://lore.kernel.org/lkml/CAKwvOd=7QTUH69+ZbT7e8einvgcosTbDkyohmPaUBv6_y8RfrQ@mail.gmail.com/ These feel more like attempts to wrap every conceivable command line flag in a kconfig option, which makes me think of that meme from Jurassic Park: "your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should." Not a fan. I'd ask for measurements, but that would be a request for a "rock fetching quest" for something I still wouldn't be a fan of. > > Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr> > --- > Makefile | 5 ++++- > init/Kconfig | 8 ++++++++ > 2 files changed, 12 insertions(+), 1 deletion(-) > > diff --git a/Makefile b/Makefile > index 1f8bef92868f..14467386f947 100644 > --- a/Makefile > +++ b/Makefile > @@ -817,7 +817,10 @@ KBUILD_CFLAGS += $(call cc-disable-warning, format-truncation) > KBUILD_CFLAGS += $(call cc-disable-warning, format-overflow) > KBUILD_CFLAGS += $(call cc-disable-warning, address-of-packed-member) > > -ifdef CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE > +ifdef CONFIG_CC_OPTIMIZE_FOR_COMPILATION_SPEED > +KBUILD_CFLAGS += -O1 > +KBUILD_RUSTFLAGS_OPT_LEVEL_MAP := 1 > +else ifdef CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE > KBUILD_CFLAGS += -O2 > KBUILD_RUSTFLAGS_OPT_LEVEL_MAP := 2 > else ifdef CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3 > diff --git a/init/Kconfig b/init/Kconfig > index a96776a9b080..3177a1830c9a 100644 > --- a/init/Kconfig > +++ b/init/Kconfig > @@ -1384,6 +1384,14 @@ choice > prompt "Compiler optimization level" > default CC_OPTIMIZE_FOR_PERFORMANCE > > +config CC_OPTIMIZE_FOR_COMPILATION_SPEED > + bool "Optimize for compilation speed (-O1)" > + help > + This option can be useful when running a static checker such as smatch > + or a build-bot. > + Compilation time is slighly faster than -O2 and it requires less s/slighly/slightly/ > + memory. > + > config CC_OPTIMIZE_FOR_PERFORMANCE > bool "Optimize for performance (-O2)" > help > -- > 2.34.1 >
Le 23/05/2022 à 20:26, Nick Desaulniers a écrit : > On Sat, May 21, 2022 at 2:04 AM Christophe JAILLET > <christophe.jaillet@wanadoo.fr> wrote: >> >> Add a new compilation option which speeds-up compilation time. >> This can be useful when using static checker such as smatch or build-bots. >> In such cases, the speed and quality of the generated code is not >> important. >> >> Using -O0 would be even better, but unfortunately, building fails with >> this option. > > Which is a tragedy. > > As with the Rust series, I'm not a fan of this (or > CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3): > https://lore.kernel.org/lkml/CAKwvOd=7QTUH69+ZbT7e8einvgcosTbDkyohmPaUBv6_y8RfrQ@mail.gmail.com/ > > These feel more like attempts to wrap every conceivable command line > flag in a kconfig option, which makes me think of that meme from > Jurassic Park: "your scientists were so preoccupied with whether or > not they could, they didn't stop to think if they should." > Not a fan. I'd ask for measurements, but that would be a request for > a "rock fetching quest" for something I still wouldn't be a fan of. Hi, some preliminary tests gave roughly a 5% build time speed-up with -O1. That is to say that the impact seems quite limited, after all. This was done on building /drivers/net/ or /drivers/net/ethernet/ only. I don't have numbers for the impact on memory consumption. Given the feedbacks on -O1 which is unlikely to be able to build a full kernel and your position on yet another option for a very specific use case, I won't push the idea further. I'll keep it in my own tree for (small) build time improvement when running smatch. The idea of turning off a subset of -O2 options would just be some too fine tuning. I'll certainly try it for my own use, but it would end to an un-understandable list of flags in Makefile. -O1 (or -O0) was simple. A more complex solution is way too much. Thanks for your feedbacks. CJ > >> >> Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr> >> --- >> Makefile | 5 ++++- >> init/Kconfig | 8 ++++++++ >> 2 files changed, 12 insertions(+), 1 deletion(-) >> >> diff --git a/Makefile b/Makefile >> index 1f8bef92868f..14467386f947 100644 >> --- a/Makefile >> +++ b/Makefile >> @@ -817,7 +817,10 @@ KBUILD_CFLAGS += $(call cc-disable-warning, format-truncation) >> KBUILD_CFLAGS += $(call cc-disable-warning, format-overflow) >> KBUILD_CFLAGS += $(call cc-disable-warning, address-of-packed-member) >> >> -ifdef CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE >> +ifdef CONFIG_CC_OPTIMIZE_FOR_COMPILATION_SPEED >> +KBUILD_CFLAGS += -O1 >> +KBUILD_RUSTFLAGS_OPT_LEVEL_MAP := 1 >> +else ifdef CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE >> KBUILD_CFLAGS += -O2 >> KBUILD_RUSTFLAGS_OPT_LEVEL_MAP := 2 >> else ifdef CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3 >> diff --git a/init/Kconfig b/init/Kconfig >> index a96776a9b080..3177a1830c9a 100644 >> --- a/init/Kconfig >> +++ b/init/Kconfig >> @@ -1384,6 +1384,14 @@ choice >> prompt "Compiler optimization level" >> default CC_OPTIMIZE_FOR_PERFORMANCE >> >> +config CC_OPTIMIZE_FOR_COMPILATION_SPEED >> + bool "Optimize for compilation speed (-O1)" >> + help >> + This option can be useful when running a static checker such as smatch >> + or a build-bot. >> + Compilation time is slighly faster than -O2 and it requires less > > s/slighly/slightly/ Thanks for taking time for a full review, even on something you are not fan on. This is really appreciated. CJ > >> + memory. >> + >> config CC_OPTIMIZE_FOR_PERFORMANCE >> bool "Optimize for performance (-O2)" >> help >> -- >> 2.34.1 >> > >
Hi Christophe, On Mon, May 23, 2022 at 9:11 AM Christophe JAILLET <christophe.jaillet@wanadoo.fr> wrote: > > +KBUILD_RUSTFLAGS_OPT_LEVEL_MAP := 1 The patch seems based on linux-next -- is this intended? Thanks! Cheers, Miguel
On Mon, May 23, 2022 at 1:16 PM Christophe JAILLET <christophe.jaillet@wanadoo.fr> wrote: > > Thanks for taking time for a full review, even on something you are not > fan on. This is really appreciated. Of course! It's still a question worth asking, and having a lore link to refer back to should the question arise again in the future. Thanks for asking.
Le 23/05/2022 à 22:25, Miguel Ojeda a écrit : > Hi Christophe, > > On Mon, May 23, 2022 at 9:11 AM Christophe JAILLET > <christophe.jaillet@wanadoo.fr> wrote: >> >> +KBUILD_RUSTFLAGS_OPT_LEVEL_MAP := 1 > > The patch seems based on linux-next -- is this intended? Thanks! Yes, I work on -next. Honestly, this "RUST flag" was just a mimic of the KBUILD_CFLAGS. No real opinion on it, I just put something that looked consistent for a patch that was only a RFC. CJ > > Cheers, > Miguel >
On Mon, May 23, 2022 at 8:27 PM Nick Desaulniers <ndesaulniers@google.com> wrote: > > As with the Rust series, I'm not a fan of this (or > CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3): > https://lore.kernel.org/lkml/CAKwvOd=7QTUH69+ZbT7e8einvgcosTbDkyohmPaUBv6_y8RfrQ@mail.gmail.com/ I think it should be decided whether we want extra levels or not, and apply that policy to both the C and Rust sides. If we don't, then yeah, let's remove them in both sides and just let users modify `CFLAGS` as needed. If we do, then having them as config options makes sense so that they can be kept working. Cheers, Miguel
On Mon, May 23, 2022 at 10:44 PM Christophe JAILLET <christophe.jaillet@wanadoo.fr> wrote: > > Yes, I work on -next. > > Honestly, this "RUST flag" was just a mimic of the KBUILD_CFLAGS. > No real opinion on it, I just put something that looked consistent for a > patch that was only a RFC. Understood, thanks! Cheers, Miguel
diff --git a/Makefile b/Makefile index 1f8bef92868f..14467386f947 100644 --- a/Makefile +++ b/Makefile @@ -817,7 +817,10 @@ KBUILD_CFLAGS += $(call cc-disable-warning, format-truncation) KBUILD_CFLAGS += $(call cc-disable-warning, format-overflow) KBUILD_CFLAGS += $(call cc-disable-warning, address-of-packed-member) -ifdef CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE +ifdef CONFIG_CC_OPTIMIZE_FOR_COMPILATION_SPEED +KBUILD_CFLAGS += -O1 +KBUILD_RUSTFLAGS_OPT_LEVEL_MAP := 1 +else ifdef CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE KBUILD_CFLAGS += -O2 KBUILD_RUSTFLAGS_OPT_LEVEL_MAP := 2 else ifdef CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3 diff --git a/init/Kconfig b/init/Kconfig index a96776a9b080..3177a1830c9a 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -1384,6 +1384,14 @@ choice prompt "Compiler optimization level" default CC_OPTIMIZE_FOR_PERFORMANCE +config CC_OPTIMIZE_FOR_COMPILATION_SPEED + bool "Optimize for compilation speed (-O1)" + help + This option can be useful when running a static checker such as smatch + or a build-bot. + Compilation time is slighly faster than -O2 and it requires less + memory. + config CC_OPTIMIZE_FOR_PERFORMANCE bool "Optimize for performance (-O2)" help
Add a new compilation option which speeds-up compilation time. This can be useful when using static checker such as smatch or build-bots. In such cases, the speed and quality of the generated code is not important. Using -O0 would be even better, but unfortunately, building fails with this option. Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr> --- Makefile | 5 ++++- init/Kconfig | 8 ++++++++ 2 files changed, 12 insertions(+), 1 deletion(-)