Re: [PATCH] x86/rapl: Do not load in a guest

From	"H. Peter Anvin" <hpa@zytor.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH] x86/rapl: Do not load in a guest
Date	2015-12-04 23:50 +0100
Message-ID	<qC7kR-l8-13@gated-at.bofh.it> (permalink)
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On December 4, 2015 2:14:46 PM PST, Peter Zijlstra <peterz@infradead.org> wrote:
>On Fri, Dec 04, 2015 at 09:51:02AM -0800, Jacob Pan wrote:
>> On Fri, 4 Dec 2015 09:22:56 +0100
>> Peter Zijlstra <peterz@infradead.org> wrote:
>> 
>> > Also, yuck @ powercap/intel_rapl.c for doing rdmsr_on_cpu() +
>> > wrmsr_on_cpu() all over the place.
>> Can you please be more specific? is the concern related to the
>> overhead of IPI? I am doing these calls based on MSR CPU scope and
>> consider the fact that access is less frequent.
>
>Yeah, its just offensive to do an IPI to read a value, then twiddle a
>few bits on the value and then IPI again to store the value.
>
>I know its low freq, and that MSR access is slow, but *groan*.

Yes, for that it would be better to invoke a common routine to do all the accesses on the target CPU.  MSR accesses may be slow, but IPIs are way slower.
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[PATCH] x86/rapl: Do not load in a guest Borislav Petkov <bp@alien8.de> - 2015-12-03 19:30 +0100
  Re: [PATCH] x86/rapl: Do not load in a guest Jacob Pan <jacob.jun.pan@linux.intel.com> - 2015-12-03 19:40 +0100
    Re: [PATCH] x86/rapl: Do not load in a guest Borislav Petkov <bp@alien8.de> - 2015-12-03 19:50 +0100
      Re: [PATCH] x86/rapl: Do not load in a guest Jacob Pan <jacob.jun.pan@linux.intel.com> - 2015-12-03 20:10 +0100
        Re: [PATCH] x86/rapl: Do not load in a guest "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2015-12-04 00:10 +0100
          Re: [PATCH] x86/rapl: Do not load in a guest Borislav Petkov <bp@alien8.de> - 2015-12-04 00:30 +0100
            Re: [PATCH] x86/rapl: Do not load in a guest "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2015-12-04 01:40 +0100
  Re: [PATCH] x86/rapl: Do not load in a guest Ingo Molnar <mingo@kernel.org> - 2015-12-04 08:50 +0100
    Re: [PATCH] x86/rapl: Do not load in a guest Ingo Molnar <mingo@kernel.org> - 2015-12-04 09:30 +0100
      Re: [PATCH] x86/rapl: Do not load in a guest Borislav Petkov <bp@alien8.de> - 2015-12-04 11:30 +0100
        Re: [PATCH] x86/rapl: Do not load in a guest Paolo Bonzini <pbonzini@redhat.com> - 2015-12-04 11:50 +0100
          Re: [PATCH] x86/rapl: Do not load in a guest Borislav Petkov <bp@alien8.de> - 2015-12-04 12:00 +0100
            Re: [PATCH] x86/rapl: Do not load in a guest Ingo Molnar <mingo@kernel.org> - 2015-12-04 13:00 +0100
              Re: [PATCH] x86/rapl: Do not load in a guest Jacob Pan <jacob.jun.pan@linux.intel.com> - 2015-12-04 18:50 +0100
                Re: [PATCH] x86/rapl: Do not load in a guest Paolo Bonzini <pbonzini@redhat.com> - 2015-12-04 19:00 +0100
                Re: [PATCH] x86/rapl: Do not load in a guest Borislav Petkov <bp@alien8.de> - 2015-12-04 19:10 +0100
                Re: [PATCH] x86/rapl: Do not load in a guest Jacob Pan <jacob.jun.pan@linux.intel.com> - 2015-12-04 19:20 +0100
                Re: [PATCH] x86/rapl: Do not load in a guest Borislav Petkov <bp@alien8.de> - 2015-12-04 19:30 +0100
                Re: [PATCH] x86/rapl: Do not load in a guest Jacob Pan <jacob.jun.pan@linux.intel.com> - 2015-12-04 19:50 +0100
                Re: [PATCH] x86/rapl: Do not load in a guest Borislav Petkov <bp@alien8.de> - 2015-12-04 20:50 +0100
    Re: [PATCH] x86/rapl: Do not load in a guest Peter Zijlstra <peterz@infradead.org> - 2015-12-04 09:30 +0100
      Re: [PATCH] x86/rapl: Do not load in a guest Jacob Pan <jacob.jun.pan@linux.intel.com> - 2015-12-04 19:00 +0100
        Re: [PATCH] x86/rapl: Do not load in a guest Peter Zijlstra <peterz@infradead.org> - 2015-12-04 23:20 +0100
          Re: [PATCH] x86/rapl: Do not load in a guest "H. Peter Anvin" <hpa@zytor.com> - 2015-12-04 23:50 +0100

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