Re: Add support for limiting CPU pressure

[Paul Smith]

On Tue, 2022-12-20 at 16:59 -0500, Randy MacLeod wrote:
> > While we are doing development with Yocto Project (1), a source-
> > based Linux distro builder, we found that many instances of making
> > running in parallel with other work can overload even a large 
> > many-core build machine. Existing mechanisms that are either not
> > system-wide (-j) or are too slow(-l has 1 minute averaging), so in 
> > order to make optimal use of a multi-core system for some larger
> > tasks we need a new mechanism.

Can you clarify what version of GNU make you're using?

There have been a number of efforts to improve the accuracy of -l and
it does not (any longer) use a simple load detection, for EXACTLY this
reason (the value is too coarse, particularly at startup).

In the latest version GNU make 4.4, it will use the content of
/proc/loadavg (if it exists) to figure out how many jobs are currently
executing on the system and use that as a measurement of load.

If that's not available, we use getloadavg() but we do some math on it
to modify the load average based on the number of jobs we've started in
the last second.  Of course, this also suffers from the problem that it
only knows about jobs that THIS INSTANCE of make has started in the
last second.

Anyway you can read more about this in the comments in the source code:

https://git.savannah.gnu.org/cgit/make.git/tree/src/job.c?h=4.4#n1953