linux-kernel - Re: [PATCH 0/2] x86: Remove ideal

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Date:   Sat, 13 Mar 2021 09:49:23 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Sedat Dilek <sedat.dilek@...il.com>
Cc:     Peter Zijlstra <peterz@...radead.org>, x86@...nel.org,
        rostedt@...dmis.org, hpa@...or.com, torvalds@...uxfoundation.org,
        linux-kernel@...r.kernel.org, linux-toolchains@...r.kernel.org,
        jpoimboe@...hat.com, alexei.starovoitov@...il.com,
        mhiramat@...nel.org
Subject: Re: [PATCH 0/2] x86: Remove ideal_nops[]

On Sat, Mar 13, 2021 at 06:26:15AM +0100, Sedat Dilek wrote:
> x86/jump_label: Mark arguments as const to satisfy asm constraints

Where do I find this patch?

> x86: Remove dynamic NOP selection
> objtool,x86: Use asm/nops.h
> 
> My benchmark was to build a Linux-kernel with LLVM/Clang v12.0.0-rc3
> on Debian/testing AMD64.
> 
> Patchset applied for a first build:
> 
>  Performance counter stats for 'make V=1 -j4 LLVM=1 LLVM_IAS=1
> PAHOLE=/opt/pahole/bin/pahole LOCALVERSION=-7-amd64-clang12-cfi
> KBUILD_VERBOSE=1 KBUILD_BUILD_HOST=iniza

There's a reason I have -s for silent in the build - printing output
during the build creates a *lot* of variance. And you have excessive
printing with V=1 and KBUILD_VERBOSE=1.

Also, you need to repeat those workloads a couple of times - one is not
enough. That's why I have --repeat 5 in there.

Also, you need --pre=/root/bin/pre-build-kernel.sh where that script is:

---
#!/bin/bash
echo $0

make -s clean
echo 3 > /proc/sys/vm/drop_caches
---

so that you can avoid pagecache influence.

Lemme rerun here with clang.

-- 
Regards/Gruss,
    Boris.

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