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

Wed Jan 30 11:09:23 PST 2013

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
>>>>
>>