linux-kernel - Re: [PATCH 08/10] x86-64: select DYNAMIC_DEBUG_RELATIVE

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Date:   Wed, 10 Apr 2019 09:31:40 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, x86@...nel.org,
        Jason Baron <jbaron@...mai.com>, linux-kernel@...r.kernel.org,
        Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH 08/10] x86-64: select DYNAMIC_DEBUG_RELATIVE_POINTERS


* Rasmus Villemoes <linux@...musvillemoes.dk> wrote:

> This reduces the size of struct _ddebug from 56 to 40 bytes. There's
> one such struct for each pr_debug(), netdev_debug() etc. in a
> CONFIG_DYNAMIC_DEBUG kernel. An Ubuntu 4.15 kernel has about 2550
> entries in the __verbose section of vmlinux, amounting to ~40K
> saved. (Modules also become smaller, but it's harder to quantify how
> much that yields at runtime.)
> 
> For comparison, the __bug_table section of that Ubuntu kernel is 75576
> bytes, i.e. 6298 12-byte bug_entrys, so GENERIC_BUG_RELATIVE_POINTERS
> saves ~50K.
> 
> Due to the build-time sanity checks in asm-generic/dynamic_debug.h, we
> need to add another #undef to vclock_gettime.c.
> 
> Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
> ---
>  arch/x86/Kconfig                            | 1 +
>  arch/x86/entry/vdso/vdso32/vclock_gettime.c | 1 +
>  arch/x86/include/asm/Kbuild                 | 1 +
>  3 files changed, 3 insertions(+)
> 
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 5ad92419be19..eb5488b4577d 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -30,6 +30,7 @@ config X86_64
>  	select SWIOTLB
>  	select X86_DEV_DMA_OPS
>  	select ARCH_HAS_SYSCALL_WRAPPER
> +	select DYNAMIC_DEBUG_RELATIVE_POINTERS

Acked-by: Ingo Molnar <mingo@...nel.org>

Thanks,

	Ingo