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Re: /proc/cpuinfo vs. processor groups




THanks for the report but this belongs to the cygwin ML.
I'm redirecting this here.


Corinna

On Apr 10 18:36, Achim Gratz wrote:
> 
> As briefly discussed on IRC I've got a new Server 2016 blade with 2
> sockets × 8 cores × 2 HT =32 logical processors and Cygwin spews errors
> for processor ID 16 and up (also top doesn't quite work, which likely
> has the same reason, although the code path may be unrelated to the
> /proc/cpuinfo bug described here).
> 
> --8<---------------cut here---------------start------------->8---
> 64bit (166)~ > cat /proc/cpuinfo
>       0 [main] cat 10068 format_proc_cpuinfo: SetThreadGroupAffinity(10000,0 (10/16)) failed Win32 error 87
>     209 [main] cat 10068 format_proc_cpuinfo: SetThreadGroupAffinity(20000,0 (11/17)) failed Win32 error 87
>     913 [main] cat 10068 format_proc_cpuinfo: SetThreadGroupAffinity(40000,0 (12/18)) failed Win32 error 87
>    1047 [main] cat 10068 format_proc_cpuinfo: SetThreadGroupAffinity(80000,0 (13/19)) failed Win32 error 87
>    1151 [main] cat 10068 format_proc_cpuinfo: SetThreadGroupAffinity(100000,0 (14/20)) failed Win32 error 87
>    1266 [main] cat 10068 format_proc_cpuinfo: SetThreadGroupAffinity(200000,0 (15/21)) failed Win32 error 87
>    1383 [main] cat 10068 format_proc_cpuinfo: SetThreadGroupAffinity(400000,0 (16/22)) failed Win32 error 87
>    1479 [main] cat 10068 format_proc_cpuinfo: SetThreadGroupAffinity(800000,0 (17/23)) failed Win32 error 87
>    1573 [main] cat 10068 format_proc_cpuinfo: SetThreadGroupAffinity(1000000,0 (18/24)) failed Win32 error 87
>    1675 [main] cat 10068 format_proc_cpuinfo: SetThreadGroupAffinity(2000000,0 (19/25)) failed Win32 error 87
>    1806 [main] cat 10068 format_proc_cpuinfo: SetThreadGroupAffinity(4000000,0 (1A/26)) failed Win32 error 87
>    1888 [main] cat 10068 format_proc_cpuinfo: SetThreadGroupAffinity(8000000,0 (1B/27)) failed Win32 error 87
>    1971 [main] cat 10068 format_proc_cpuinfo: SetThreadGroupAffinity(10000000,0 (1C/28)) failed Win32 error 87
>    2069 [main] cat 10068 format_proc_cpuinfo: SetThreadGroupAffinity(20000000,0 (1D/29)) failed Win32 error 87
>    2154 [main] cat 10068 format_proc_cpuinfo: SetThreadGroupAffinity(40000000,0 (1E/30)) failed Win32 error 87
>    2247 [main] cat 10068 format_proc_cpuinfo: SetThreadGroupAffinity(80000000,0 (1F/31)) failed Win32 error 87
> --8<---------------cut here---------------end--------------->8---
> 
> It turns out this is related to processor groups and some changes that
> probably weren't even in the making when the Cygwin code was written.
> These changes were opt-in patches until 2008R2, but are now the default
> in 2016:
> 
> https://blogs.msdn.microsoft.com/saponsqlserver/2011/10/08/uneven-windows-processor-groups/
> 
> The BIOS on that server does something rather peculiar (it does make
> sense in a way, but Cygwin clearly didn't expect it):
> 
> https://support.hpe.com/hpsc/doc/public/display?sp4ts.oid=7271227&docId=emr_na-c04650594&docLocale=en_US
> 
> This results in Windows coming up with two 64 core processor groups that
> have 16 active logical processors each:
> 
> --8<---------------cut here---------------start------------->8---
> (gdb) print plpi
> $1 = (PSYSTEM_LOGICAL_PROCESSOR_INFORMATION_EX) 0x600008020
> (gdb) print *plpi
> $2 = {Relationship = RelationGroup, Size = 128, {Processor = {Flags = 2 '\002', Reserved = "\000\002", '\000' <repeats 18 times>, GroupCount = 0,
>       GroupMask = {{Mask = 4160, Group = 0, Reserved = {0, 0, 0}}}}, NumaNode = {NodeNumber = 131074, Reserved = '\000' <repeats 19 times>,
>       GroupMask = {Mask = 4160, Group = 0, Reserved = {0, 0, 0}}}, Cache = {Level = 2 '\002', Associativity = 0 '\000', LineSize = 2, CacheSize = 0,
>       Type = CacheUnified, Reserved = '\000' <repeats 12 times>, "@\020\000\000\000\000\000", GroupMask = {Mask = 0, Group = 0, Reserved = {0, 0,
>           0}}}, Group = {MaximumGroupCount = 2, ActiveGroupCount = 2, Reserved = '\000' <repeats 19 times>, GroupInfo = {{
>           MaximumProcessorCount = 64 '@', ActiveProcessorCount = 16 '\020', Reserved = '\000' <repeats 37 times>, ActiveProcessorMask = 65535}}}}}
> --8<---------------cut here---------------end--------------->8---
> 
> I've confirmed that the error message is not printed if I manually
> correct the information for processor ID 17 as follows:
> 
> --8<---------------cut here---------------start------------->8---
> (gdb) print affinity                                                                                                                                                            
> $2 = {Mask = 131072, Group = 0, Reserved = {0, 0, 0}}                                                                                                                           
> (gdb) set affinity.Mask=2                                                                                                                                                       
> (gdb) set affinity.Group=1
> --8<---------------cut here---------------end--------------->8---
> 
> However, the same or possibly even stranger processor group setups can
> be created using boot options that force different organizations of
> processor groups.  There is an option to force a seperate processor
> group for each NUMA node and another one to force a specific number of
> groups.  The upshot is that even the first processor groups may not have
> the maximum number of processors present, so you need to check the
> number of active processors instead.  I couldn't find out if the
> processor mask is still guaranteed to be filled from the LSB contigously
> or whether one can rely on only the last group to have less than the
> first few.  It seems more prudent to check the group specific
> ActiveProcessorMask, although that significantly complicates the code.
> I don't think Windows can currently switch CPU online/offline when
> booted.
> 
> 
> As an aside, the cache size is reported as 256kiB (not just for this
> processor, but also for a Celeron 1037U on another machine), which seems
> to be the L2 cache for a single hardware core on these architectures.
> Linux now reports L3 cache sizes (and possibly L4 if present) for these
> (20MiB and 2MiB per socket respectively).
> 
> 
> Regards,
> Achim.
> --
> +<[Q+ Matrix-12 WAVE#46+305 Neuron microQkb Andromeda XTk Blofeld]>+
> 
> Factory and User Sound Singles for Waldorf Blofeld:
> http://Synth.Stromeko.net/Downloads.html#WaldorfSounds

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
Red Hat

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