PATCH: enable PAT at Pentium M 1.7 GHz - Kernel

This is a discussion on PATCH: enable PAT at Pentium M 1.7 GHz - Kernel ; Hi there, Sending oneliner enabling PAT at my Pentium M 1.7 GHz CPU. It simply works. Thanks for inclusion: --- linux-2.6.26.2/arch/x86/kernel/cpu/addon_cpuid_features.c 2008-08-08 21:52:20.000000000 +0200 +++ linux-2.6.26.2/arch/x86/kernel/cpu/addon_cpuid_features.c 2008-08-08 21:41:17.000000000 +0200 @@ -59,7 +59,7 @@ return; break; case X86_VENDOR_INTEL: - if (c->x86 ...

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Thread: PATCH: enable PAT at Pentium M 1.7 GHz

  1. PATCH: enable PAT at Pentium M 1.7 GHz

    Hi there,

    Sending oneliner enabling PAT at my Pentium M 1.7 GHz CPU. It simply works.
    Thanks for inclusion:

    --- linux-2.6.26.2/arch/x86/kernel/cpu/addon_cpuid_features.c
    2008-08-08 21:52:20.000000000 +0200
    +++ linux-2.6.26.2/arch/x86/kernel/cpu/addon_cpuid_features.c 2008-08-08
    21:41:17.000000000 +0200
    @@ -59,7 +59,7 @@
    return;
    break;
    case X86_VENDOR_INTEL:
    - if (c->x86 == 0xF || (c->x86 == 6 && c->x86_model >= 15))
    + if (c->x86 == 0xF || (c->x86 == 6 && c->x86_model >= 13))
    return;
    break;
    }

    Listik:/usr/src# cat /proc/cpuinfo
    processor : 0
    vendor_id : GenuineIntel
    cpu family : 6
    model : 13
    model name : Intel(R) Pentium(R) M processor 1.70GHz
    stepping : 6
    cpu MHz : 600.000
    cache size : 2048 KB
    fdiv_bug : no
    hlt_bug : no
    f00f_bug : no
    coma_bug : no
    fpu : yes
    fpu_exception : yes
    cpuid level : 2
    wp : yes
    flags : fpu vme de pse tsc msr mce cx8 apic sep mtrr pge mca cmov
    pat clflush dts acpi mmx fxsr sse sse2 ss tm pbe bts est tm2
    bogomips : 1200.47
    clflush size : 64
    power management:


    before:
    Aug 8 19:08:27 Listik kernel: PAT disabled. Not yet verified on this CPU
    type.


    after:
    Aug 8 21:43:34 Listik kernel: x86 PAT enabled: cpu 0, old 0x7040600070406,
    new 0x7010600070106

    Bye

    Michal
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  2. Re: PATCH: enable PAT at Pentium M 1.7 GHz

    CIJOML wrote:
    > Hi there,
    > Sending oneliner enabling PAT at my Pentium M 1.7 GHz CPU. It simply works.


    That's not really the right way to do that. Unfortunately the likely
    failure scenario is "data corruption after a month of uptime." Thus, we
    really need someone to review the relevant errata; I believe Venki is
    planning to do so.

    -hpa
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  3. Re: PATCH: enable PAT at Pentium M 1.7 GHz

    H. Peter Anvin writes:

    > CIJOML wrote:
    >> Hi there,
    >> Sending oneliner enabling PAT at my Pentium M 1.7 GHz CPU. It simply
    >> works.

    >
    > That's not really the right way to do that. Unfortunately the likely
    > failure scenario is "data corruption after a month of uptime." Thus, we
    > really need someone to review the relevant errata; I believe Venki is
    > planning to do so.
    >
    > -hpa


    Well the truth is, that I use this little tweak from 2.6.26-rc and first cpu
    having PAT was P3 XEON. And because Intel has backward compatibility, it is
    safe to use it.
    I don't have any problem with loosing data or any suspend/resume problems
    with this.

    Reference:
    http://safari.ibmpressbooks.com/032124656X/ch32

    Best regards

    Michal
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  4. Re: PATCH: enable PAT at Pentium M 1.7 GHz

    CIJOML wrote:
    >
    > Well the truth is, that I use this little tweak from 2.6.26-rc and first
    > cpu having PAT was P3 XEON. And because Intel has backward
    > compatibility, it is safe to use it.
    > I don't have any problem with loosing data or any suspend/resume
    > problems with this.


    Sorry, it doesn't work that simple. There are lots of errata in CPUs,
    and data loss is too critical.

    You're of course welcome to run whatever you want on your machine, but
    we have to be more careful.

    -hpa
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  5. RE: PATCH: enable PAT at Pentium M 1.7 GHz



    >-----Original Message-----
    >From: linux-kernel-owner@vger.kernel.org
    >[mailto:linux-kernel-owner@vger.kernel.org] On Behalf Of H. Peter Anvin
    >Sent: Friday, August 08, 2008 9:34 PM
    >To: CIJOML
    >Cc: linux-kernel@vger.kernel.org; mingo@redhat.com; tglx@linutronix.de
    >Subject: Re: PATCH: enable PAT at Pentium M 1.7 GHz
    >
    >CIJOML wrote:
    >>
    >> Well the truth is, that I use this little tweak from

    >2.6.26-rc and first
    >> cpu having PAT was P3 XEON. And because Intel has backward
    >> compatibility, it is safe to use it.
    >> I don't have any problem with loosing data or any suspend/resume
    >> problems with this.

    >
    >Sorry, it doesn't work that simple. There are lots of errata in CPUs,
    >and data loss is too critical.
    >
    >You're of course welcome to run whatever you want on your machine, but
    >we have to be more careful.
    >


    Yes. I am looking through the errata list to enable PAT on known to be good CPUs.

    Unfortunately, system works fine with PAT enabled may not mean much right now.
    As there are really no significant users of PAT yet. We have PAT WC enabled in
    The kernel and PAT APIs exported for the drivers to use. But, unless there are
    very many drivers using these PAT APIs we will not really hit the erratas for
    the CPUs. Even after that, erratas are like corner cases which does not really
    happen very often. So, it is best to go by the published errata list and to
    disable PAT where there are known problems.

    Thanks,
    Venki
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