RFR(XXS): JDK-8007069 VM_Version_x86 cores per cpu is wrong for cpuid 0xb topology case

Vladimir Kozlov vladimir.kozlov at oracle.com
Wed Jan 30 10:57:55 PST 2013 

No, the example I showed has HT and VM gives correct results:

tpl_cpuidB0_ebx.bits.logical_cpus = 2
tpl_cpuidB1_ebx.bits.logical_cpus = 16

(8 cores per cpu, 2 threads per core)

Vladimir

On 1/30/13 10:47 AM, Markus Grönlund wrote:
> Hi Vladimir,
>
> Yes I have noticed that it will give ok results (so far). For example, on my Intel(R) Xeon(R) CPU E5-2690 0 @ 2.90GHz, (Sandybridge-EP).
>
> I have 8 hw threads (from os::processor_count())
>
> Also, it's using CPUID 0xb (supports topology, 2xAPICID)
>
> My values are:
>
> _cpuid_info.tpl_cpuidB0_ebx.bits.logical_cpus = 1 <<-- threads per core
> _cpuid_info.tpl_cpuidB1_ebx.bits.logical_cpus = 8 <<-- cores per cpu package
>
> Current (wrong) logic does:
>
> No of cores per cpu:
>
> Returns : _cpuid_info.tpl_cpuidB1_ebx.bits.logical_cpus = 8 / _cpuid_info.tpl_cpuidB0_ebx.bits.logical_cpus = 1 == no of cores == 8 (correct).
>
> However,
>
> This does not account for CPUs that have HT enabled, i.e  if HT is enabled, you will get this:
>
> _cpuid_info.tpl_cpuidB0_ebx.bits.logical_cpus = 2 <<-- threads per core
> _cpuid_info.tpl_cpuidB1_ebx.bits.logical_cpus = 8 <<-- cores per cpu package
>
>
> Returns : _cpuid_info.tpl_cpuidB1_ebx.bits.logical_cpus = 8 / _cpuid_info.tpl_cpuidB0_ebx.bits.logical_cpus = 2 == no of cores is now 4, but the real number of cores is 8.
>
> So, avoid doing the unnecessary divide operation (no_of_cores_per_pkg) / (no_of_threads_per_core). The correct info is already there. Just return it.
>
> Return: _cpuid_info.tpl_cpuidB1_ebx.bits.logical_cpus // 8 correct
>
>
> Cheers
> Markus
>
>
>
> -----Original Message-----
> From: Vladimir Kozlov
> Sent: den 30 januari 2013 19:33
> To: Markus Grönlund
> Cc: Mikael Vidstedt; hotspot-dev at openjdk.java.net
> Subject: Re: RFR(XXS): JDK-8007069 VM_Version_x86 cores per cpu is wrong for cpuid 0xb topology case
>
> Markus,
>
> Current code is correct. In what case it is not correct?
>
> bash-4.1$ psrinfo -pv
> The physical processor has 8 cores and 16 virtual processors (0-7 16-23)
>     The core has 2 virtual processors (0 16)
>     The core has 2 virtual processors (1 17)
>     The core has 2 virtual processors (2 18)
>     The core has 2 virtual processors (3 19)
>     The core has 2 virtual processors (4 20)
>     The core has 2 virtual processors (5 21)
>     The core has 2 virtual processors (6 22)
>     The core has 2 virtual processors (7 23)
>       x86 (GenuineIntel 206D6 family 6 model 45 step 6 clock 2693 MHz)
>         Intel(r) Xeon(r) CPU E5-2680 0 @ 2.70GHz
>
> ash-4.1$ java -XX:+PrintMiscellaneous -XX:+Verbose -version [SafePoint Polling address: 0xfffffd7fff1e0000] [Memory Serialize  Page address: 0xfffffd7fff1d0000] Logical CPUs per core: 2
> UseSSE=4  UseAVX=1  UseAES=1
> Allocation prefetching: PREFETCHNTA at distance 192, 4 lines of 64 bytes PrefetchCopyIntervalInBytes 576 PrefetchScanIntervalInBytes 576 PrefetchFieldsAhead 1 ContendedPaddingWidth 128 CPU:total 32 (8 cores per cpu, 2 threads per core) family 6 model 45 stepping 6, cmov, cx8, fxsr, mmx, sse, sse2, sse3, ssse3, sse4.1, sse4.2, popcnt, avx, aes, ht, tsc, tscinvbit, tscinv
>
> Thanks,
> Vladimir
>
>
> On 1/30/13 9:45 AM, Markus Grönlund wrote:
>> Hi Mikael,
>>
>> I wonder if you are looking at the right section in the manual (and which manual?) here?
>>
>> I am using information in Intel Application note 485:
>>
>> http://www.intel.com/content/www/us/en/processors/processor-identifica
>> tion-cpuid-instruction-note.html
>>
>> Section 5.1.12 page 41 describes CPUID 0xb. Essentially, together with EAX=0xb, you pass in subleafs (0, 1, 2...) in ECX for the different levels in the cpu topology you are interested in. Results are given in EBX[15:0] [31:16] == reserved.
>>
>>
>> "There's also a cores_per_cpu in CPUID 04h EAX[31:26] (aka. dcp_cpuid4_eax.bits.cores_per_cpu), do you happen to know what the difference is? Is that maybe a better candidate for this?"
>>
>> CPUID04 EAX[31:26] is giving you the number of cores [per cpu package] using the legacy "initial APICID (8-bits)" systems. This combined with CPUID 01[logical threads per cpu package] is the legacy way of cpu identification. It is cannot give you as much info as topology however.
>>
>> Processors supporting CPUID 0xb is using 3-level 2xAPICID (32-bit) for identification (SMT, Core, Pkg), and does not use "initial APICID".
>>
>> So:
>>
>> EAX=0xb, ECX=0 == EBX[15:0] == no_of_logical_threads_per_core ==
>> (stored in _cpuid_info.tpl_cpuidB0_ebx.bits.logical_cpus)
>> EAX=0xb, ECX=1 == EBX[15:0] == no_of_cores_per_pkg == (stored in
>> _cpuid_info.tpl_cpuidB1_ebx.bits.logical_cpus)
>> ...
>>
>> Hope this clarifies
>>
>> Cheers
>> Markus
>>
>>
>>
>>
>>
>> -----Original Message-----
>> From: Mikael Vidstedt
>> Sent: den 30 januari 2013 17:30
>> To: Markus Grönlund
>> Cc: hotspot-dev at openjdk.java.net
>> Subject: Re: RFR(XXS): JDK-8007069 VM_Version_x86 cores per cpu is
>> wrong for cpuid 0xb topology case
>>
>>
>> Looking at the Intel manual for CPUID 0Bh it basically says that one should not use the value in EBX[15:0] for anything other than "...display/diagnostic purposes". There's also a cores_per_cpu in CPUID 04h EAX[31:26] (aka. dcp_cpuid4_eax.bits.cores_per_cpu), do you happen to know what the difference is? Is that maybe a better candidate for this?
>>
>> Cheers,
>> Mikael
>>
>> On 1/29/2013 2:10 AM, Markus Grönlund wrote:
>>> Hi again,
>>>
>>> Apologies for posting the wrong webrev link, this is the one I wanted to submit:
>>>
>>> Bug: https://jbs.oracle.com/bugs/browse/JDK-8007069
>>> Webrev:  http://cr.openjdk.java.net/~mgronlun/8007069/webrev01/
>>>
>>>
>>> Thanks Mikael for the heads up
>>>
>>> Cheers
>>> Markus
>>>
>>>
>>>
>>> -----Original Message-----
>>> From: Mikael Gerdin
>>> Sent: den 29 januari 2013 10:59
>>> To: Markus Grönlund
>>> Cc: hotspot-dev at openjdk.java.net
>>> Subject: Re: RFR(XXS): JDK-8007069 VM_Version_x86 cores per cpu is
>>> wrong for cpuid 0xb topology case
>>>
>>> Markus,
>>>
>>> On 2013-01-29 10:54, Markus Grönlund wrote:
>>>> Hi all,
>>>>
>>>>
>>>>
>>>> Kindly asking for review for the following very simple change in the logic for number of cores for CPUID 0xb topology.
>>>>
>>>>
>>>>
>>>> Bug: https://jbs.oracle.com/bugs/browse/JDK-8007069
>>>>
>>>> Webrev:
>>>> http://wikifiles.se.oracle.com/dev/mgronlun/webrevs/8007069/webrev01
>>>> /
>>> This URL is not available from outside Oracle.
>>>
>>> /Mikael
>>>
>>>>
>>>>
>>>> Also need someone to sponsor this putback.
>>>>
>>>>
>>>>
>>>> Thanks in advance
>>>>
>>>> Markus
>>>>
>>

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