linux-kernel - Re: [RFC PATCH v6 10/32] x86/apic: Change apic_*

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Message-ID: <20250524121537.GMaDG4adGsxaPFT7DX@fat_crate.local>
Date: Sat, 24 May 2025 14:15:37 +0200
From: Borislav Petkov <bp@...en8.de>
To: Neeraj Upadhyay <Neeraj.Upadhyay@....com>
Cc: linux-kernel@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
	dave.hansen@...ux.intel.com, Thomas.Lendacky@....com,
	nikunj@....com, Santosh.Shukla@....com, Vasant.Hegde@....com,
	Suravee.Suthikulpanit@....com, David.Kaplan@....com, x86@...nel.org,
	hpa@...or.com, peterz@...radead.org, seanjc@...gle.com,
	pbonzini@...hat.com, kvm@...r.kernel.org,
	kirill.shutemov@...ux.intel.com, huibo.wang@....com,
	naveen.rao@....com, francescolavra.fl@...il.com,
	tiala@...rosoft.com
Subject: Re: [RFC PATCH v6 10/32] x86/apic: Change apic_*_vector() vector
 param to unsigned

On Wed, May 14, 2025 at 12:47:41PM +0530, Neeraj Upadhyay wrote:
> Change vector parameter of apic_{set|clear|test}_vector to
> unsigned int to optimize code generation for modulo operation.
> 
> On gcc-14.2, code generation for below C statement is given
> after it.
> 
> long nr = APIC_VECTOR_TO_BIT_NUMBER(vec);
> 
> * Without change:
> 
>  mov    eax,edi
>  sar    eax,0x1f
>  shr    eax,0x1b
>  add    edi,eax
>  and    edi,0x1f
>  sub    edi,eax
>  movsxd rdi,edi
>  mov    QWORD PTR [rsp-0x8],rdi
> 
> * With change:
> 
>  and    edi,0x1f
>  mov    QWORD PTR [rsp-0x8],rdi

AT&T assembly please.

This change needs to go first too.

-- 
Regards/Gruss,
    Boris.

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