Re: [PATCH v2] [v2] crypto: aes-generic - fix aes-generic regression on powerpc

[Herbert Xu]

On Mon, Jan 15, 2018 at 05:07:22PM +0100, Arnd Bergmann wrote:
> My last bugfix added -Os on the command line, which unfortunately caused
> a build regression on powerpc in some configurations.
> 
> I've done some more analysis of the original problem and found slightly
> different workaround that avoids this regression and also results in
> better performance on gcc-7.0: -fcode-hoisting is an optimization step
> that got added in gcc-7 and that for all gcc-7 versions causes worse
> performance.
> 
> This disables -fcode-hoisting on all compilers that understand the option.
> For gcc-7.1 and 7.2 I found the same performance as my previous patch
> (using -Os), in gcc-7.0 it was even better. On gcc-8 I could see no
> change in performance from this patch. In theory, code hoisting should
> not be able make things better for the AES cipher, so leaving it
> disabled for gcc-8 only serves to simplify the Makefile change.
> 
> Reported-by: kbuild test robot 
> Link: https://www.mail-archive.com/linux-crypto@vger.kernel.org/msg30418.html
> Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83356
> Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83651
> Fixes: 148b974deea9 ("crypto: aes-generic - build with -Os on gcc-7+")
> Signed-off-by: Arnd Bergmann 

Patch applied.  Thanks.
-- 
Email: Herbert Xu 
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt

Re: [PATCH v2] [v2] crypto: aes-generic - fix aes-generic regression on powerpc

[Ard Biesheuvel]

On 15 January 2018 at 16:07, Arnd Bergmann  wrote:
> My last bugfix added -Os on the command line, which unfortunately caused
> a build regression on powerpc in some configurations.
>
> I've done some more analysis of the original problem and found slightly
> different workaround that avoids this regression and also results in
> better performance on gcc-7.0: -fcode-hoisting is an optimization step
> that got added in gcc-7 and that for all gcc-7 versions causes worse
> performance.
>
> This disables -fcode-hoisting on all compilers that understand the option.
> For gcc-7.1 and 7.2 I found the same performance as my previous patch
> (using -Os), in gcc-7.0 it was even better. On gcc-8 I could see no
> change in performance from this patch. In theory, code hoisting should
> not be able make things better for the AES cipher, so leaving it
> disabled for gcc-8 only serves to simplify the Makefile change.
>
> Reported-by: kbuild test robot 
> Link: https://www.mail-archive.com/linux-crypto@vger.kernel.org/msg30418.html
> Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83356
> Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83651
> Fixes: 148b974deea9 ("crypto: aes-generic - build with -Os on gcc-7+")
> Signed-off-by: Arnd Bergmann 

Acked-by: Ard Biesheuvel 

> ---
> v2: fix a typo in the Makefile
> ---
>  crypto/Makefile | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/crypto/Makefile b/crypto/Makefile
> index daa69360e054..cdbc03b35510 100644
> --- a/crypto/Makefile
> +++ b/crypto/Makefile
> @@ -99,7 +99,7 @@ obj-$(CONFIG_CRYPTO_TWOFISH_COMMON) += twofish_common.o
>  obj-$(CONFIG_CRYPTO_SERPENT) += serpent_generic.o
>  CFLAGS_serpent_generic.o := $(call cc-option,-fsched-pressure)  # 
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79149
>  obj-$(CONFIG_CRYPTO_AES) += aes_generic.o
> -CFLAGS_aes_generic.o := $(call cc-ifversion, -ge, 0701, -Os) # 
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83356
> +CFLAGS_aes_generic.o := $(call cc-option,-fno-code-hoisting) # 
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83356
>  obj-$(CONFIG_CRYPTO_AES_TI) += aes_ti.o
>  obj-$(CONFIG_CRYPTO_CAMELLIA) += camellia_generic.o
>  obj-$(CONFIG_CRYPTO_CAST_COMMON) += cast_common.o
> --
> 2.9.0
>

[PATCH v2] [v2] crypto: aes-generic - fix aes-generic regression on powerpc

[Arnd Bergmann]

My last bugfix added -Os on the command line, which unfortunately caused
a build regression on powerpc in some configurations.

I've done some more analysis of the original problem and found slightly
different workaround that avoids this regression and also results in
better performance on gcc-7.0: -fcode-hoisting is an optimization step
that got added in gcc-7 and that for all gcc-7 versions causes worse
performance.

This disables -fcode-hoisting on all compilers that understand the option.
For gcc-7.1 and 7.2 I found the same performance as my previous patch
(using -Os), in gcc-7.0 it was even better. On gcc-8 I could see no
change in performance from this patch. In theory, code hoisting should
not be able make things better for the AES cipher, so leaving it
disabled for gcc-8 only serves to simplify the Makefile change.

Reported-by: kbuild test robot 
Link: https://www.mail-archive.com/linux-crypto@vger.kernel.org/msg30418.html
Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83356
Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83651
Fixes: 148b974deea9 ("crypto: aes-generic - build with -Os on gcc-7+")
Signed-off-by: Arnd Bergmann 
---
v2: fix a typo in the Makefile
---
 crypto/Makefile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/crypto/Makefile b/crypto/Makefile
index daa69360e054..cdbc03b35510 100644
--- a/crypto/Makefile
+++ b/crypto/Makefile
@@ -99,7 +99,7 @@ obj-$(CONFIG_CRYPTO_TWOFISH_COMMON) += twofish_common.o
 obj-$(CONFIG_CRYPTO_SERPENT) += serpent_generic.o
 CFLAGS_serpent_generic.o := $(call cc-option,-fsched-pressure)  # 
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79149
 obj-$(CONFIG_CRYPTO_AES) += aes_generic.o
-CFLAGS_aes_generic.o := $(call cc-ifversion, -ge, 0701, -Os) # 
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83356
+CFLAGS_aes_generic.o := $(call cc-option,-fno-code-hoisting) # 
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83356
 obj-$(CONFIG_CRYPTO_AES_TI) += aes_ti.o
 obj-$(CONFIG_CRYPTO_CAMELLIA) += camellia_generic.o
 obj-$(CONFIG_CRYPTO_CAST_COMMON) += cast_common.o
-- 
2.9.0