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

Wed Jan 30 11:26:29 PST 2013

You are welcome.

Yes, you have to read "small print" not only on financial documents but 
also in hw architecture manuals :(

Regards,
Vladimir

On 1/30/13 11:09 AM, Markus Grönlund wrote:
> Vladimir,
>
> many thanks giving me a good example, I have only had _cpuid_info.tpl_cpuidB0_ebx.bits.logical_cpus = 1, so far.
>
> You are right, thank you for showing me this, I did not read the details on the Note2 on Core level well enough:
>
> "2. The number of factory-configured logical processors at this level is equal to the number of factory-configured cores * the number of factory-configured logical processors per core."
>
> It was my (mis)understanding that Core level did not multiply up to the SMT level(but id does as the note gives as well as your example explains).
>
> Many thanks Vladimir
>
> Cheers
> Markus
>
>
>
> -----Original Message-----
> From: Vladimir Kozlov
> Sent: den 30 januari 2013 19:58
> 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
>
> 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-identific
>>> a
>>> 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/webrev0
>>>>> 1
>>>>> /
>>>> This URL is not available from outside Oracle.
>>>>
>>>> /Mikael
>>>>
>>>>>
>>>>>
>>>>> Also need someone to sponsor this putback.
>>>>>
>>>>>
>>>>>
>>>>> Thanks in advance
>>>>>
>>>>> Markus
>>>>>
>>>