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From: Borislav Petkov <bp@alien8.de>
To: torvic9@mailbox.org
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"x86@kernel.org" <x86@kernel.org>,
	"clang-built-linux@googlegroups.com" 
	<clang-built-linux@googlegroups.com>,
	"graysky@archlinux.us" <graysky@archlinux.us>,
	"masahiroy@kernel.org" <masahiroy@kernel.org>,
	Christoph Hellwig <hch@infradead.org>
Subject: Re: [PATCH 2/2] x86, Makefile: Add new generic x86-64 settings v2/v3/v4
Date: Wed, 18 Aug 2021 19:59:00 +0200	[thread overview]
Message-ID: <YR1KDD/azm1IDr9u@zn.tnic> (raw)
In-Reply-To: <1708009975.124311.1629299321026@office.mailbox.org>

On Wed, Aug 18, 2021 at 05:08:40PM +0200, torvic9@mailbox.org wrote:
> I ran some quick checks and benchmarks, and your doubts seem to be
> justified. A 5.14-rc6 kernel compiled with the default 'generic' and
> one built with 'x86-64-v3' even have the exact same uncompressed file
> size. Benchmarks were inconclusive as well.

Lemme preface this with a IMHO:

Yeah, those -march machine-specific compiler switches don't really
show any perf improvements for kernels because, well, if you look at
the instruction stream a kernel executes, there's not really a whole
lot left to optimize after -O2.

Also, the percentage of time a machine spends in the kernel should be a
lot smaller (orders of magnitude) than in userspace - the operative word
being *should* here :-) - so there really isn't anything to optimize.

Not to say that there aren't a gazillion other places in the kernel that
could use more eyes and testing. ^Hint hint^

Thx.

-- 
Regards/Gruss,
    Boris.

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

  reply	other threads:[~2021-08-18 17:58 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-17 14:23 [PATCH 1/2] x86, Makefile: Move the CPU-specific 64-bit tuning settings to arch/x86/Makefile.cpu torvic9
2021-08-17 14:24 ` [PATCH 2/2] x86, Makefile: Add new generic x86-64 settings v2/v3/v4 torvic9
2021-08-17 18:17   ` Nick Desaulniers
2021-08-17 18:22     ` Nick Desaulniers
2021-08-17 18:31       ` Tor Vic
2021-08-17 18:47         ` Nick Desaulniers
2021-08-17 18:36   ` Borislav Petkov
2021-08-17 19:12     ` Tor Vic
2021-08-18 15:08     ` torvic9
2021-08-18 17:59       ` Borislav Petkov [this message]
2021-08-18 18:28         ` Tor Vic
2021-08-18 18:43           ` Borislav Petkov
2021-08-18  7:15   ` Christoph Hellwig
2021-08-18  9:46     ` torvic9
2021-08-19 21:58     ` David Laight
2021-08-17 17:58 ` [PATCH 1/2] x86, Makefile: Move the CPU-specific 64-bit tuning settings to arch/x86/Makefile.cpu Nick Desaulniers
2021-08-17 18:28   ` Tor Vic
2021-08-18  7:11 ` Christoph Hellwig
2021-08-18  9:46   ` torvic9
2021-08-18 14:51 ` Masahiro Yamada

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