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Subject:	Re: BUG: /usr/bin/uptime always reports 0/0/0 average
To:	cygwin AT cygwin DOT com
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From:	Cedric Blancher via Cygwin <cygwin AT cygwin DOT com>
Reply-To:	Cedric Blancher <cedric DOT blancher AT gmail DOT com>
Sender:	"Cygwin" <cygwin-bounces~archive-cygwin=delorie DOT com AT cygwin DOT com>

On Tue, 27 Aug 2024 at 18:30, Eliot Moss via Cygwin <cygwin AT cygwin DOT com> wrote:
>
> On 8/27/2024 11:31 AM, Jon Turney via Cygwin wrote:
> > On 27/08/2024 09:21, Mark Liam Brown via Cygwin wrote:
> >> Greetings!
> >>
> >> /usr/bin/uptime always reports 0/0/0 average cpu load:
> >> $ uptime
> >>   10:09:01 up 15:59,  0 user,  load average: 0.00, 0.00, 0.00
> >>
> >> is this a known bug?
> >
> > Kind of.
> >
> > Due to windows API limitations, the current implementation has the short-coming that a process's first call to
> > getloadavg() does not update the globally-maintained loadavg data.
> >
> > (Because the Windows API cannot provide instantaneous cpu load, only over the period between two calls)
> >
> > (So e.g. if you run something like top in another terminal, you'll suddenly see uptime return more sensible values)
> >
> > See the discussion [1] for more context, and discussion of various approaches to fixing this, which petered out without
> > a patch to [2]...
> >
> > [1] https://cygwin.com/pipermail/cygwin-developers/2022-May/012569.html
> > [2] https://cygwin.com/cgit/newlib-cygwin/tree/winsup/cygwin/loadavg.cc
>
> Thank you for the explanation, Mark!
>
> I see that /proc/loadavg appears to get updated.  If one wants the information,
> is that a more reliable source than calling uptime for load averages?

I get this on a stressed system with HUNDREDS of running processes:
$ cat /proc/loadavg
0.00 0.00 0.00 1/21

The problem is that this breaks parallel builds (e.g. GNU make, dmake,
...), which all rely on getloadavg() to cap/limit starting new
processes until the load goes below a certain threshold.
Returning just 0.0/0.0/0.0 is basically the IT equivalent for the
nuclear option: Launch more and more processes, check getloadavg(),
which returns "system is idle", which causes more and more processes
being started, until the machine grinds to a halt for interactive
users.
That is... pretty bad.

Ced
-- 
Cedric Blancher <cedric DOT blancher AT gmail DOT com>
[https://plus.google.com/u/0/+CedricBlancher/]
Institute Pasteur

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