Re: load average calculation failing

Re: load average calculation failing

[Jon Turney]

On 08/05/2022 08:01, Mark Geisert wrote:
> Mark Geisert wrote (on the main Cygwin mailing list):
>> I've recently noticed that the 'xload' I routinely run shows zero load 
>> even with compute-bound processes running.  This is on both Cygwin 
>> pre-3.4.0 as well as 3.3.4.  A test program, shown below, indicates 
>> that getloadavg() is returning with 0 status, i.e. not an error but no 
>> elems
>> of the passed-in array updated.
>>
>> Stepping with gdb through the test program seems weird within the 
>> loadavginfo::load_init method.  Single-stepping at line loadavg.cc:68 
>> goes to strace.h:52 and then to _sigbe ?!
>>
>> I had recently updated both Cygwin and Windows 10 to latest at the 
>> same time so I cannot say when the failure started.  Last day or two 
>> at most.
>>
[...]
> 
> I've debugged a bit further..  Within Cygwin's loadavg.cc:load_init(), 
> the PdhOpenQueryW() call returns successfully.  The subsequent 
> PdhAddEnglishCounterW() call is unsuccessful.  It returns status 
> 0x800007D0 == PDH_CSTATUS_NO_MACHINE. The code (at line 68 mentioned 
> above) calls debug_printf() to conditionally display the error, which is 
> what leads to the strace.h and _sigbe; that's fine.
> 
> The weird PDH_CSTATUS_NO_MACHINE is the problem.  I'll try running the 
> example from an elevated shell.  Or rebooting the machine.  After that 
> it's consulting some oracle TBD. :-(
> 

Thanks for looking into this.
You can find the user space version of this code I initially wrote at 
https://github.com/jon-turney/windows-loadavg, which might save you some 
time.

I can't reproduce this on W10 21H1, so I think this must be due to some 
change in later Windows...