[PATCH] Implement getloadavg()
Jon Turney
jon.turney@dronecode.org.uk
Tue Mar 21 13:56:00 GMT 2017
On 20/03/2017 15:40, Corinna Vinschen wrote:
> On Mar 20 15:04, Jon Turney wrote:
>> On 20/03/2017 10:37, Corinna Vinschen wrote:
>>> On Mar 17 17:50, Jon Turney wrote:
>>> The load average is global, non-critical data. So what about storing it
>>> in shared_info instead? This way, only the first call of the first
>>> Cygwin process returns all zero.
>>
>> Ok.
>>
>>>> +static bool load_init (void)
>>>> +{
>>>> + static bool tried = false;
>>>> + static bool initialized = false;
>>>> +
>>>> + if (!tried) {
>>>> + tried = true;
>>>> +
>>>> + if ((PdhOpenQueryA (NULL, 0, &query) == ERROR_SUCCESS) &&
>>>> + (PdhAddEnglishCounterA (query, "\\Processor(_Total)\\% Processor Time",
>>>> + 0, &counter1) == ERROR_SUCCESS) &&
>>>> + (PdhAddEnglishCounterA (query, "\\System\\Processor Queue Length",
>>>> + 0, &counter2) == ERROR_SUCCESS)) {
>>>> + initialized = true;
>>>> + } else {
>>>> + debug_printf("loadavg PDH initialization failed\n");
>>>> + }
>>>> + }
>>>> +
>>>> + return initialized;
>>>> +}
>>>
>>> How slow is that initialization? Would it {make sense|hurt} to call it
>>> once in the initalization of Cygwin's shared mem in shared_info::initialize?
>>
>> I don't think that's particularly heavyweight, and I didn't see anything to
>> suggest that PDH query handles can be shared between processes, but I'll
>> look into it.
>
> Oh, right, that might pose a problem.
I can't find anything which documents these handles as shareable.
In practise, they seem to randomly stop working after a while after the
process which created the handle exits, or something like that. :S
> But even then:
>
> The first process creating shared_info could call this and prime the values
> with a first call to getloadavg. Each other process would have to init its
We cannot determine an initial value of load when shared_info is
created, as the %CPU is not measured instantaneously, but over an
interval. This means that we can't have a load estimate until the 2nd
time a process calls PdhCollectQueryData()
I've tweaked things slightly in v2 so the loadavg is initialized to the
current load, rather than converging on it from 0.0.
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