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Re: [tip:x86/urgent] x86/cpu: Use indirect call to measure performance in init_amd_k6()

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On Wed, 12 Jul 2017, Borislav Petkov wrote:

> On Wed, Jul 12, 2017 at 06:09:57AM -0700, tip-bot for Mikulas Patocka wrote:
> > Commit-ID:  429ed86b5c99b388543f6f7f6983b1230326f2bb
> > Gitweb:     http://git.kernel.org/tip/429ed86b5c99b388543f6f7f6983b1230326f2bb
> > Author:     Mikulas Patocka <mpatocka@redhat.com>
> > AuthorDate: Tue, 11 Jul 2017 07:44:05 -0400
> > Committer:  Ingo Molnar <mingo@kernel.org>
> > CommitDate: Wed, 12 Jul 2017 10:42:32 +0200
> > 
> > x86/cpu: Use indirect call to measure performance in init_amd_k6()
> > 
> > This old piece of code is supposed to measure the performance of indirect
> > calls to determine if the processor is buggy or not, however the compiler
> > optimizer turns it into a direct call.
> 
> Are you booting on a real K6 or qemu?

I tested it on K6-3 and it doesn't trigger the warning, the loop with the 
indirect call takes 9 million cycles (it took 4 million cycles with the 
direct call).

I don't have the old K6 revision with the bug.

Mikulas

> -- 
> Regards/Gruss,
>     Boris.
> 
> ECO tip #101: Trim your mails when you reply.
> --

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[PATCH] x86/kernel/cpu/amd.c: use indirect call Mikulas Patocka <mpatocka@redhat.com> - 2017-07-11 13:50 +0200
  [tip:x86/urgent] x86/cpu: Use indirect call to measure performance  in init_amd_k6() tip-bot for Mikulas Patocka <tipbot@zytor.com> - 2017-07-12 15:20 +0200
    Re: [tip:x86/urgent] x86/cpu: Use indirect call to measure  performance in init_amd_k6() Borislav Petkov <bp@alien8.de> - 2017-07-12 15:50 +0200
      Re: [tip:x86/urgent] x86/cpu: Use indirect call to measure performance  in init_amd_k6() Mikulas Patocka <mpatocka@redhat.com> - 2017-07-13 04:30 +0200
  [tip:x86/urgent] x86/cpu: Use indirect call to measure performance  in init_amd_k6() tip-bot for Mikulas Patocka <tipbot@zytor.com> - 2017-07-16 11:30 +0200

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