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Re: [PATCH] x86: Implement __WARN using UD0

From Arjan van de Ven <arjan@linux.intel.com>
Newsgroups linux.kernel
Subject Re: [PATCH] x86: Implement __WARN using UD0
Date 2017-02-23 15:20 +0100
Message-ID <te2pr-2oI-1@gated-at.bofh.it> (permalink)
References <te1D4-1LK-9@gated-at.bofh.it>
Organization linux.* mail to news gateway

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On 2/23/2017 5:28 AM, Peter Zijlstra wrote:
>
> By using "UD0" for WARNs we remove the function call and its possible
> __FILE__ and __LINE__ immediate arguments from the instruction stream.
>
> Total image size will not change much, what we win in the instruction
> stream we'll loose because of the __bug_table entries. Still, saves on
> I$ footprint and the total image size does go down a bit.

well I am a little sceptical; WARNs are rare so the code (other than the test)
should be waaay out of line already (unlikely() and co).
And I assume you're not removing the __FILE__ and __LINE__ info, since that info
is actually high value for us developers... so what are you actually saving?

(icache saving is only real if the line that the cold code lives on would actually
end up in icache for other reasons; I would hope the compiler puts the out
of line code WAY out of line)

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Thread

[PATCH] x86: Implement __WARN using UD0 Peter Zijlstra <peterz@infradead.org> - 2017-02-23 14:30 +0100
  Re: [PATCH] x86: Implement __WARN using UD0 Arjan van de Ven <arjan@linux.intel.com> - 2017-02-23 15:20 +0100
    Re: [PATCH] x86: Implement __WARN using UD0 Peter Zijlstra <peterz@infradead.org> - 2017-02-23 16:00 +0100
      Re: [PATCH] x86: Implement __WARN using UD0 Ingo Molnar <mingo@kernel.org> - 2017-02-24 09:00 +0100
        Re: [PATCH] x86: Implement __WARN using UD0 Peter Zijlstra <peterz@infradead.org> - 2017-02-24 09:40 +0100
          Re: [PATCH] x86: Implement __WARN using UD0 Ingo Molnar <mingo@kernel.org> - 2017-02-24 10:20 +0100
            Re: [PATCH] x86: Implement __WARN using UD0 Borislav Petkov <bp@alien8.de> - 2017-02-24 10:50 +0100
              Re: [PATCH] x86: Implement __WARN using UD0 "H. Peter Anvin" <hpa@zytor.com> - 2017-02-24 12:50 +0100
            Re: [PATCH] x86: Implement __WARN using UD0 Peter Zijlstra <peterz@infradead.org> - 2017-02-24 12:50 +0100
              Re: [PATCH] x86: Implement __WARN using UD0 Borislav Petkov <bp@alien8.de> - 2017-02-25 11:50 +0100
                Re: [PATCH] x86: Implement __WARN using UD0 hpa@zytor.com - 2017-02-25 19:00 +0100
                Re: [PATCH] x86: Implement __WARN using UD0 Borislav Petkov <bp@alien8.de> - 2017-02-25 20:40 +0100
                Re: [PATCH] x86: Implement __WARN using UD0 Borislav Petkov <bp@alien8.de> - 2017-02-25 21:40 +0100
                Re: [PATCH] x86: Implement __WARN using UD0 hpa@zytor.com - 2017-02-25 21:50 +0100
          Re: [PATCH] x86: Implement __WARN using UD0 hpa@zytor.com - 2017-02-24 10:20 +0100
          Re: [PATCH] x86: Implement __WARN using UD0 hpa@zytor.com - 2017-02-24 10:50 +0100
  Re: [PATCH] x86: Implement __WARN using UD0 Peter Zijlstra <peterz@infradead.org> - 2017-02-23 15:20 +0100
    Re: [PATCH] x86: Implement __WARN using UD0 Peter Zijlstra <peterz@infradead.org> - 2017-02-23 16:00 +0100
    Re: [PATCH] x86: Implement __WARN using UD0 hpa@zytor.com - 2017-02-23 16:20 +0100
      Re: [PATCH] x86: Implement __WARN using UD0 Peter Zijlstra <peterz@infradead.org> - 2017-02-23 16:30 +0100
        Re: [PATCH] x86: Implement __WARN using UD0 hpa@zytor.com - 2017-02-23 16:40 +0100
          Re: [PATCH] x86: Implement __WARN using UD0 Borislav Petkov <bp@alien8.de> - 2017-02-23 17:10 +0100
  Re: [PATCH] x86: Implement __WARN using UD0 Josh Poimboeuf <jpoimboe@redhat.com> - 2017-02-23 15:20 +0100
    Re: [PATCH] x86: Implement __WARN using UD0 Borislav Petkov <bp@alien8.de> - 2017-02-23 15:30 +0100
    Re: [PATCH] x86: Implement __WARN using UD0 Peter Zijlstra <peterz@infradead.org> - 2017-02-23 15:40 +0100
  [PATCH -v2] x86: Implement __WARN using UD0 Peter Zijlstra <peterz@infradead.org> - 2017-02-24 12:20 +0100
    [RFC][PATCH] bug: Add _ONCE logic to report_bug() Peter Zijlstra <peterz@infradead.org> - 2017-02-25 10:10 +0100
      Re: [RFC][PATCH] bug: Add _ONCE logic to report_bug() Ingo Molnar <mingo@kernel.org> - 2017-02-25 10:20 +0100
        Re: [RFC][PATCH] bug: Add _ONCE logic to report_bug() Peter Zijlstra <peterz@infradead.org> - 2017-02-25 11:50 +0100

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