posix thread scaling issue

[jeff]

On 9/2/2023 10:56, Brian Inglis wrote:
> On 2023-09-02 08:57, jeff via Cygwin wrote:
>> I have a program that is embarrassing parallel.
>> On my older computer which has an epyc 7302 (16 cores,  32 threads) 
>> it scales very well using cygwin, and fully utilized all threads.
>> On my new computer which has an epyc 7B13 (64 cores, 128 threads) it 
>> does not scale very well.
>>
>> According to the windows task manager, it only uses 74% of the cpu 
>> resources.
>> The time it takes the program to run on windows is 166 seconds.
>> Using the same hardware on a recent version of linux, I can get 100% 
>> cpu utilization and the program takes 100 seconds to run.
>>
>> I suspect there may be something in cygwin that doesn't scale well 
>> with lots of posix threads.
>> I know this is a bit of an unusual situation, but you can buy a 128 
>> core / 256 thread system now.
>>
>> Enclosed is the output of cygcheck.
>> I updated my version of cygwin to be current as of today, Sep 2 2023.
>
> What Windows edition and version are you running?
> For details run:
>
> $ reg query "HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows 
> NT\CurrentVersion" \
> | sed '/^\s\+\.*\s/!d;/^.\{80,\}/d'
>
> Some retail editions limit you to 64 threads and that seems to be your 
> case:
>
>     NUMBER_OF_PROCESSORS = '64'
>
> To make full use of your processors, you may have to upgrade your 
> Windows to a commercial licence (and installation) of Windows 10/11 
> Pro for Workstations, enabling server features on non-server 
> "Worskations" ~ HEDTs (High-End DeskTops); see:
>
> https://www.anandtech.com/show/15483/amd-threadripper-3990x-review/3
>
> or just run Linux!
>
> Watch out for terms misused like processor == socket on some sites!
>
> Also, you have to consider these are server systems, mainly designed 
> for VM not HPC (High Performance Computing) parallelism.
>
> Your older system has higher base and boost/turbo clocks 3.0-3.3GHz: 
> your newer system has lower clocks 2.25-2.65/3/3.5GHz which seems to 
> depend on OEM target.
>
> You may also need to upgrade your memory, as each core could run 
> ~10GB/s instructions, and these workstations are often provisioned 
> with 128-256GB (2-4GB/core), so that may also need a Windows edition 
> upgrade.
I am running windows 10 professional. Using the task manager, 64 cores 
and 128 threads shows up for my processor.

Here is the output of your regex:
     SystemRoot    REG_SZ    C:\Windows
     BaseBuildRevisionNumber    REG_DWORD    0x1
     BuildBranch    REG_SZ    vb_release
     BuildGUID    REG_SZ    ffffffff-ffff-ffff-ffff-ffffffffffff
     BuildLab    REG_SZ    19041.vb_release.191206-1406
     BuildLabEx    REG_SZ    19041.1.amd64fre.vb_release.191206-1406
     CompositionEditionID    REG_SZ    Enterprise
     CurrentBuild    REG_SZ    19045
     CurrentBuildNumber    REG_SZ    19045
     CurrentMajorVersionNumber    REG_DWORD    0xa
     CurrentMinorVersionNumber    REG_DWORD    0x0
     CurrentType    REG_SZ    Multiprocessor Free
     CurrentVersion    REG_SZ    6.3
     EditionID    REG_SZ    Professional
     EditionSubManufacturer    REG_SZ
     EditionSubstring    REG_SZ
     EditionSubVersion    REG_SZ
     InstallationType    REG_SZ    Client
     InstallDate    REG_DWORD    0x61e2300a
     ProductName    REG_SZ    Windows 10 Pro
     ReleaseId    REG_SZ    2009
     SoftwareType    REG_SZ    System
     UBR    REG_DWORD    0xcfc
     PathName    REG_SZ    C:\Windows
     ProductId    REG_SZ    00330-80000-00000-AA073
     DisplayVersion    REG_SZ    22H2
     RegisteredOwner    REG_SZ    jdeifik
     RegisteredOrganization    REG_SZ
     InstallTime    REG_QWORD    0x1d809b6d4ce7b09

In practice, but the new and old processors typically run at about 3ghz 
when under load.
When idling, both processors use about the same amount of power.

I have 128gb of ram, in 4 slots. Using that configuration, I can get 
100% load and significant faster performance on linux.
Therefore I conclude the issue is either with windows or cygwin, and is 
not a hardware issue.
When I run cinebench, I can get to 100% cpu utulization (at around 3ghz) 
on windows.

As for what the processors are 'designed' for, I really don't care.
I want a reliable, fast computer with ECC memory, and I can get that 
with an EPYC processor.
If a workload needs more than 128gb of memory, you pretty much need to 
use server processors.
I can put in up to 2tb of memory in my system, if I have the need for that.

jeff