linux-kernel - Re: [PATCHv11 18/19] x86/acpi: Add support for CPU offlining for ACPI MADT wakeup method

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Date: Fri, 14 Jun 2024 09:06:30 -0500
From: Tom Lendacky <thomas.lendacky@....com>
To: Borislav Petkov <bp@...en8.de>,
 "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
 "Rafael J. Wysocki" <rafael@...nel.org>,
 Peter Zijlstra <peterz@...radead.org>,
 Adrian Hunter <adrian.hunter@...el.com>,
 Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>,
 Elena Reshetova <elena.reshetova@...el.com>,
 Jun Nakajima <jun.nakajima@...el.com>,
 Rick Edgecombe <rick.p.edgecombe@...el.com>,
 "Kalra, Ashish" <ashish.kalra@....com>,
 Sean Christopherson <seanjc@...gle.com>, "Huang, Kai" <kai.huang@...el.com>,
 Ard Biesheuvel <ardb@...nel.org>, Baoquan He <bhe@...hat.com>,
 "H. Peter Anvin" <hpa@...or.com>, "K. Y. Srinivasan" <kys@...rosoft.com>,
 Haiyang Zhang <haiyangz@...rosoft.com>, kexec@...ts.infradead.org,
 linux-hyperv@...r.kernel.org, linux-acpi@...r.kernel.org,
 linux-coco@...ts.linux.dev, linux-kernel@...r.kernel.org,
 Tao Liu <ltao@...hat.com>
Subject: Re: [PATCHv11 18/19] x86/acpi: Add support for CPU offlining for ACPI
 MADT wakeup method

On 6/13/24 09:56, Borislav Petkov wrote:
> On Thu, Jun 13, 2024 at 04:41:00PM +0300, Kirill A. Shutemov wrote:
>> It is easy enough to do. See the patch below.
> 
> Thanks, will have a look.
> 
>> But I am not sure if I can justify it properly. If someone doesn't really
>> need 5-level paging, disabling it at compile-time would save ~34K of
>> kernel code with the configuration.
>>
>> Is it worth saving ~100 lines of code?
> 
> Well, it goes both ways: is it worth saving ~34K kernel text and for that make
> the code a lot less conditional, more readable, contain less ugly ifdeffery,

Won't getting rid of the config option cause 5-level to be used by default 
on all platforms that support it? The no5lvl command line option would 
have to be used to get 4-level paging at that point.

Thanks,
Tom

> ...?
>