linux-kernel - Re: [PATCH v2 1/2] x86: make VMware support optional

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Message-ID: <20201203074631.GC3059@zn.tnic>
Date:   Thu, 3 Dec 2020 08:46:59 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     "Enrico Weigelt, metux IT consult" <info@...ux.net>
Cc:     linux-kernel@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
        x86@...nel.org, hpa@...or.com, dmitry.torokhov@...il.com,
        derek.kiernan@...inx.com, dragan.cvetic@...inx.com,
        richardcochran@...il.com, linux-hyperv@...r.kernel.org,
        linux-input@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH v2 1/2] x86: make VMware support optional

On Wed, Dec 02, 2020 at 10:19:48PM +0100, Enrico Weigelt, metux IT consult wrote:
> Make it possible to opt-out from VMware support, for minimized kernels
> that never will be run under Vmware (eg. high-density virtualization
> or embedded systems).
> 
> Average distro kernel will leave it on, therefore default to y.
> 
> Signed-off-by: Enrico Weigelt <info@...ux.net>
> ---
>  arch/x86/Kconfig                 | 11 +++++++++++
>  arch/x86/kernel/cpu/Makefile     |  4 +++-
>  arch/x86/kernel/cpu/hypervisor.c |  2 ++
>  drivers/input/mouse/Kconfig      |  2 +-
>  drivers/misc/Kconfig             |  2 +-
>  drivers/ptp/Kconfig              |  2 +-
>  6 files changed, 19 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index f6946b81f74a..eff12460cb3c 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -801,6 +801,17 @@ config X86_HV_CALLBACK_VECTOR
>  
>  source "arch/x86/xen/Kconfig"
>  
> +config VMWARE_GUEST
> +	bool "VMware Guest support"
> +	default y
> +	help
> +	  This option enables several optimizations for running under the
> +	  VMware hypervisor.
> +
> +	  Disabling it saves a few kb, for stripped down kernels eg. in high

I was actually expecting for you to do your own measurements and show data.
Anyway, I did it for you:

   text    data     bss     dec     hex filename
15949304        127806978       36597916        180354198       abffc96 vmlinux.before
15947650        127802430       36602012        180352092       abff45c vmlinux.after

this is with my .config.

How much is it with a stripped down kernel? I bet it is even less. Which
makes this whole effort not worth it...

Also, when you send a new version of your patches, please rework *all*
review feedback you've received on the previous one.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette