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Bug 162144

Summary:	[MBS] Parallel optimal number could be better
Product:	[Tools] CDT	Reporter:	Doug Schaefer <cdtdoug>
Component:	cdt-build-managed	Assignee:	Project Inbox <cdt-build-managed-inbox>
Status:	RESOLVED DUPLICATE	QA Contact:	Chris Recoskie <recoskie>
Severity:	normal
Priority:	P3	CC:	jensseidel, recoskie
Version:	4.0
Target Milestone:	---
Hardware:	PC
OS:	Windows XP
Whiteboard:

Description Doug Schaefer

2006-10-24 16:59:41 EDT

In most make manuals when they talk about the -j option to parallelize make builds, they say that the optimal job number is the number of processors plus one. I notice that when I choose the optimal number on my single processor system, I see the number used is 1. I think 2 might be more optimal since a compile is often waiting on disk IO and could share the CPU.

Comment 1 Eric Hildum

2007-05-23 14:48:20 EDT

On my dual core system, the optimal number is also 1 by default. It appears that this is a static value, and not a very good default under any circumstances.

Comment 2 Jens Seidel

2009-06-16 07:02:55 EDT

I even noticed that Eclipse creates sometimes a load of 300 and more on my Linux system!!!!! In such a case the box is just frozen and completely unresponsive. If I'm lucky and are able to have a running process viewer I see 20-30 compiler jobs in parallel. That's too much even for a quad core CPU.

The affected project is a Managed C++ project where Eclipse creates the Makefiles and there are currently three builds performed (Debug, Release and a test build). If Eclipse chooses 2*number of cores as default per each build and runs all builds together it would result in such large job numbers.

Using -j3 fixes this.

The severity of this bug should be increased as often a reboot is the only practical solution (waiting a few few hours may also help but as the system doesn't react fast enough even a ssh connection to kill processes doesn't help).

Comment 3 Chris Recoskie

2009-06-16 09:50:53 EDT

I thought the "optimal" number we were using *was* the number of processors +1?

I guess it's not... but it should be.

Comment 4 Jens Seidel

2009-06-17 11:10:38 EDT

(In reply to comment #3)
> I thought the "optimal" number we were using *was* the number of processors +1?
> 
> I guess it's not... but it should be.

Probably you know that ordinary make evaluates a variable MAKEFLAGS which I set to j8 ... But in this case I start only a single make process.

Comment 5 Andrew Gvozdev

2010-03-24 22:02:18 EDT

closing as duplicate

*** This bug has been marked as a duplicate of bug 259768 ***