linux-kernel - Re: i686 quirk for AMD Geode

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Message-ID: <40101cc30910030253w70adc454r1bb38ff4424c7b14@mail.gmail.com>
Date:	Sat, 3 Oct 2009 11:53:39 +0200
From:	Matteo Croce <technoboy85@...il.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org
Subject: Re: i686 quirk for AMD Geode

On Sat, Oct 3, 2009 at 9:21 AM, Ingo Molnar <mingo@...e.hu> wrote:
>
> * Matteo Croce <technoboy85@...il.com> wrote:
>
>> Hi,
>>
>> the AMD GEode LX has an x86 id of 5 (i586) tought it's technically an i686:
>>
>> root@...x:/usr/src# cat /proc/cpuinfo
>> processor       : 0
>> vendor_id       : AuthenticAMD
>> cpu family      : 5
>> model           : 10
>> model name      : Geode(TM) Integrated Processor by AMD PCS
>> stepping        : 2
>> cpu MHz         : 498.060
>> cache size      : 128 KB
>> fdiv_bug        : no
>> hlt_bug         : no
>> f00f_bug        : no
>> coma_bug        : no
>> fpu             : yes
>> fpu_exception   : yes
>> cpuid level     : 1
>> wp              : yes
>> flags           : fpu de pse tsc msr cx8 sep pge cmov clflush mmx
>> mmxext 3dnowext 3dnow
>> bogomips        : 996.12
>> clflush size    : 32
>> cache_alignment : 32
>> address sizes   : 32 bits physical, 32 bits virtual
>> power management:
>>
>> indeed it has mmx, mmxext and cmov.
>> So I added the quirk below and I can confirm that the system is running fine.
>> I did an x264 encode to trigger any SIGILL due to missing opcodes, but
>> it worked.
>>
>> I also did this simple test which gives a ~2.5x speed boost:
>> http://pastebin.ca/1590089
>>
>> I wish some feedback from someone, I really dunno why AMD set the
>> cpuid value to 5
>>
>> --- a/arch/x86/kernel/cpu/bugs.c      2009-10-03 03:43:02.399323313 +0200
>> +++ b/arch/x86/kernel/cpu/bugs.c      2009-10-03 03:54:22.582205090 +0200
>> @@ -151,6 +151,12 @@
>>  #endif
>>  }
>>
>> +static void __init check_geode_i586(void)
>> +{
>> +     if(boot_cpu_data.x86_vendor == X86_VENDOR_AMD &&
>> +        boot_cpu_data.x86_model == 10 && boot_cpu_data.x86 == 5)
>> +             boot_cpu_data.x86 = 6;
>> +}
>>
>>  void __init check_bugs(void)
>>  {
>> @@ -163,6 +169,7 @@
>>       check_fpu();
>>       check_hlt();
>>       check_popad();
>> +     check_geode_i586();
>>       init_utsname()->machine[1] =
>>               '0' + (boot_cpu_data.x86 > 6 ? 6 : boot_cpu_data.x86);
>>       alternative_instructions();
>
> Looks good, but your signoff line is missing.
>
>        Ingo
>

Sorry Ingo but if you read my last mail I wrote that the GEODE does
supports FCOMI but not NOPL
so i don't know if it's worth it, even is I haven't ANY binary in my
system with such instruction:

# find /lib/tls/i686 /lib/i686 -type f |xargs objdump -d |grep -c nopl
0
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