[Buildroot] [PATCH] package-infra: limit the number of // jobs

[Yann E. MORIN <yann.morin.1998@free.fr>]

Nathan, All,

On Fri, May 10, 2013 at 08:09:11AM -0500, Nathan Lynch wrote:
> On Fri, 2013-05-10 at 00:03 +0200, Yann E. MORIN wrote:
> > From: "Yann E. MORIN" <yann.morin.1998@free.fr>
> > 
> > The current code spawns as many jobs as up to twice the number of CPUs.
> > 
> > On small-class machines like laptops, with a limitted amount of memory,
> > but still a few CPUs (real or hyperthreads), the HDD becomes a bottleneck,
> > and it becomes almost impossible to do anythiong else while there is a
> > build in progress.
> > 
> > Limit the number of jobs to the number of CPUs plus one.
> > 
> > Even on fast machines with fast HDDs, this settings keeps the machine
> > fully busy (for those packages that can build in parallel, of course).
> > 
> > For example, building qemu or the linux kernel kept my hyperthreaded
> > hexa Core i7 with 18GiB of RAM, busy at 99% (I never ever managed to
> > get 100% even with more jobs, not even 200); while on my hyperthreaded
> > dual Core i5 with only 4GiB and a slow HDD, I still topped at 100% CPU,
> > while still able to do some work involving the HDD.
> > 
> > Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
> > ---
> >  package/Makefile.in | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/package/Makefile.in b/package/Makefile.in
> > index a449089..a575f17 100644
> > --- a/package/Makefile.in
> > +++ b/package/Makefile.in
> > @@ -11,7 +11,7 @@ HOSTMAKE :=$(shell which $(HOSTMAKE) || type -p $(HOSTMAKE) || echo make)
> >  # while waiting on I/O.
> >  ifeq ($(BR2_JLEVEL),0)
> >  PARALLEL_JOBS:=$(shell echo \
> > -	$$((2 * `getconf _NPROCESSORS_ONLN 2>/dev/null || echo 1`)))
> > +	$$((2 + `getconf _NPROCESSORS_ONLN 2>/dev/null || echo 0`)))
> 
> You'll need to update/remove the comment preceding this code too...

Right, good catch. I'll send an updated patch soonish.

> When I submitted this feature there was some discussion of what the
> heuristic should be here.  Given your experience I am fine with making
> it more conservative, especially since this is the default behavior.

Yes. In the Good Old Times (TM), it was customary to set jobs=2*CPU,
because disks (or network) was very slow, and IO did not catch up with
CPU bandwidth; this is not much true these days.

Regards,
Yann E. MORIN.

-- 
.-----------------.--------------------.------------------.--------------------.
|  Yann E. MORIN  | Real-Time Embedded | /"\ ASCII RIBBON | Erics' conspiracy: |
| +33 662 376 056 | Software  Designer | \ / CAMPAIGN     |  ___               |
| +33 223 225 172 `------------.-------:  X  AGAINST      |  \e/  There is no  |
| http://ymorin.is-a-geek.org/ | _/*\_ | / \ HTML MAIL    |   v   conspiracy.  |
'------------------------------^-------^------------------^--------------------'