This is the mail archive of the cygwin-patches mailing list for the Cygwin project.

Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

Re: [PATCH] Implement getloadavg()

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.


+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.

Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]