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Date: Fri, 14 Jun 2024 09:06:30 -0500
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Subject: Re: [PATCHv11 18/19] x86/acpi: Add support for CPU offlining for ACPI
 MADT wakeup method
To: Borislav Petkov <bp@alien8.de>,
 "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
 Dave Hansen <dave.hansen@linux.intel.com>, x86@kernel.org,
 "Rafael J. Wysocki" <rafael@kernel.org>,
 Peter Zijlstra <peterz@infradead.org>,
 Adrian Hunter <adrian.hunter@intel.com>,
 Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>,
 Elena Reshetova <elena.reshetova@intel.com>,
 Jun Nakajima <jun.nakajima@intel.com>,
 Rick Edgecombe <rick.p.edgecombe@intel.com>,
 "Kalra, Ashish" <ashish.kalra@amd.com>,
 Sean Christopherson <seanjc@google.com>, "Huang, Kai" <kai.huang@intel.com>,
 Ard Biesheuvel <ardb@kernel.org>, Baoquan He <bhe@redhat.com>,
 "H. Peter Anvin" <hpa@zytor.com>, "K. Y. Srinivasan" <kys@microsoft.com>,
 Haiyang Zhang <haiyangz@microsoft.com>, kexec@lists.infradead.org,
 linux-hyperv@vger.kernel.org, linux-acpi@vger.kernel.org,
 linux-coco@lists.linux.dev, linux-kernel@vger.kernel.org,
 Tao Liu <ltao@redhat.com>
References: <20240528095522.509667-19-kirill.shutemov@linux.intel.com>
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From: Tom Lendacky <thomas.lendacky@amd.com>
In-Reply-To: <20240613145636.GGZmsIpHn16R04QlaN@fat_crate.local>
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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

> ...?
>