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 <[email protected]>
---
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 Sat, May 21, 2022 at 2:04 AM Christophe JAILLET
<[email protected]> 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 <[email protected]>
> ---
> 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
>
--
Thanks,
~Nick Desaulniers
On Mon, May 23, 2022 at 1:16 PM Christophe JAILLET
<[email protected]> 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.
--
Thanks,
~Nick Desaulniers
Le 23/05/2022 à 22:25, Miguel Ojeda a écrit :
> Hi Christophe,
>
> On Mon, May 23, 2022 at 9:11 AM Christophe JAILLET
> <[email protected]> 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
>
Hi Christophe,
On Mon, May 23, 2022 at 9:11 AM Christophe JAILLET
<[email protected]> wrote:
>
> +KBUILD_RUSTFLAGS_OPT_LEVEL_MAP := 1
The patch seems based on linux-next -- is this intended? Thanks!
Cheers,
Miguel
Le 23/05/2022 à 20:26, Nick Desaulniers a écrit :
> On Sat, May 21, 2022 at 2:04 AM Christophe JAILLET
> <[email protected]> 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 <[email protected]>
>> ---
>> 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
>>
>
>
On Mon, May 23, 2022 at 8:27 PM Nick Desaulniers
<[email protected]> 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
<[email protected]> 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