load average calculation failing -- fixed by Windows update

[Jon Turney]

On 13/05/2022 12:05, Corinna Vinschen wrote:
> On May 13 13:04, Corinna Vinschen wrote:
>> On May 13 11:34, Jon Turney wrote:
>>> On 12/05/2022 10:48, Corinna Vinschen wrote:
>>>> On May 11 16:40, Mark Geisert wrote:
>>>>>
>>>>> The first counter read now gets error 0xC0000BC6 == PDH_INVALID_DATA, but no
>>>>> errors on subsequent counter reads.  This sounds like it now matches what
>>>>> Corinna reported for W11.  I wonder if she's running build 1706 already.
>>>>
>>>> Erm... looks like I didn't read your mail throughly enough.
>>>>
>>>> This behaviour, the first call returning with PDH_INVALID_DATA and only
>>>> subsequent calls returning valid(?) values, is what breaks the
>>>> getloadavg function and, consequentially, /proc/loadavg.  So maybe xload
>>>> now works, but Cygwin is still broken.
>>>
>>> The first attempt to read '% Processor Time' is expected to fail with
>>> PDH_INVALID_DATA, since it doesn't have a value at a particular instant, but
>>> one averaged over a period of time.
>>>
>>> This is what the following comment is meant to record:
>>>
>>> "Note that PDH will only return data for '% Processor Time' after the second
>>> call to PdhCollectQueryData(), as it's computed over an interval, so the
>>> first attempt to estimate load will fail and 0.0 will be returned."
>>
>> But.
>>
>> Every invocation of getloadavg() returns 0.  Even under load.  Calling
>> `cat /proc/loadavg' is an excercise in futility.
>>
>> The only way to make getloadavg() work is to call it in a loop from the
>> same process with a 1 sec pause between invocations.  In that case, even
>> a parallel `cat /proc/loadavg' shows the same load values.
>>
>> However, as soon as I stop the looping process, the /proc/loadavg values
>> are frozen in the last state they had when stopping that process.
> 
> Oh, and, stopping and restarting all Cygwin processes in the session will
> reset the loadavg to 0.
> 
>> Any suggestions how to fix this?

Ah, right.  'while true ; do cat /proc/loadavg ; done', just shows a 
stream of zeroes, because each process only calls getloadavg() once, 
which doesn't update the loadavg, because the first call to fetch it 
fails PDH_INVALID_DATA.

This isn't really simply fixable because PDH "handles" aren't shareable 
between processes.

I don't think this is new since it is mentioned in [1].

Non-solution: use top instead :)

[1] https://cygwin.com/pipermail/cygwin-patches/2017q1/008699.html