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From: Linus Torvalds <torvalds@linux-foundation.org>
To: David Laight <David.Laight@aculab.com>
Cc: Noah Goldstein <goldstein.w.n@gmail.com>,
	kernel test robot <lkp@intel.com>,
	 "x86@kernel.org" <x86@kernel.org>,
	 "oe-kbuild-all@lists.linux.dev" <oe-kbuild-all@lists.linux.dev>,
	 "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"edumazet@google.com" <edumazet@google.com>,
	 "tglx@linutronix.de" <tglx@linutronix.de>,
	"mingo@redhat.com" <mingo@redhat.com>,
	"bp@alien8.de" <bp@alien8.de>,
	 "dave.hansen@linux.intel.com" <dave.hansen@linux.intel.com>,
	"hpa@zytor.com" <hpa@zytor.com>
Subject: Re: x86/csum: Remove unnecessary odd handling
Date: Fri, 5 Jan 2024 16:18:43 -0800	[thread overview]
Message-ID: <CAHk-=wjGaH6oA47WkphTweMiy15Zjfuk-aVcXSasMX=aX9rFLQ@mail.gmail.com> (raw)
In-Reply-To: <204bf145e6ad47219c005e9a4407ebdc@AcuMS.aculab.com>

On Fri, 5 Jan 2024 at 15:53, David Laight <David.Laight@aculab.com> wrote:
>
> I'd have to fix his benchmark code first :-)
> You can't use the TSC unless you lock the cpu frequency.
> The longer the test runs for the faster the cpu will run.

They'll stabilize, it has soem cycle result aging code.

But yes, set the CPU policy to 'performance' or do performance
counters if you care deeply.

> On a related point, do you remember what the 'killer app'
> was for doing the checksum in copy_to/from_user?

No. It's a long time ago, and many things have changed since.

It's possible the copy-and-csum it's not worth it any more, simply
because all modern network cards will do the csum for us, and I think
loopback sets a flag saying "no need to checksum" too.

But I do have a strong memory of it being a big deal back when. A
_loong_ time ago.

          Linus

  reply	other threads:[~2024-01-06  0:19 UTC|newest]

Thread overview: 33+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20230628020657.957880-1-goldstein.w.n@gmail.com>
2023-06-28  9:12 ` x86/csum: Remove unnecessary odd handling Borislav Petkov
2023-06-28 15:32   ` Noah Goldstein
2023-06-28 17:44     ` Linus Torvalds
2023-06-28 18:34       ` Noah Goldstein
2023-06-28 20:02         ` Linus Torvalds
2023-06-29 14:04   ` David Laight
2023-06-29 14:27   ` David Laight
2023-09-01 22:21 ` Noah Goldstein
2023-09-06 13:49   ` David Laight
2023-09-06 14:38   ` David Laight
2023-09-20 19:20     ` Noah Goldstein
2023-09-20 19:23 ` Noah Goldstein
2023-09-23  3:24   ` kernel test robot
2023-09-23 14:05     ` Noah Goldstein
2023-09-23 21:13       ` David Laight
2023-09-24 14:35         ` Noah Goldstein
2023-12-23 22:18           ` Noah Goldstein
2024-01-04 23:28             ` Noah Goldstein
2024-01-04 23:34               ` Dave Hansen
2024-01-04 23:36               ` Linus Torvalds
2024-01-05  0:33                 ` Linus Torvalds
2024-01-05 10:41                   ` David Laight
2024-01-05 16:12                     ` David Laight
2024-01-05 18:05                     ` Linus Torvalds
2024-01-05 23:52                       ` David Laight
2024-01-06  0:18                         ` Linus Torvalds [this message]
2024-01-06 10:26                           ` Eric Dumazet
2024-01-06 19:32                             ` Linus Torvalds
2024-01-07 12:11                             ` David Laight
2024-01-06 22:08                       ` David Laight
2024-01-07  1:09                         ` H. Peter Anvin
2024-01-07 11:44                           ` David Laight
2023-09-24 14:35 ` Noah Goldstein

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