Messages in this thread | | | Date | Mon, 23 May 2022 22:16:05 +0200 | Subject | Re: [RFC PATCH] kbuild: Add an option to enable -O1 and speed-up compilation time | From | Christophe JAILLET <> |
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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 >> > >
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