[U-Boot] [PATCH] MAKEALL: Automatically use parallel builds

[Wolfgang Denk]

Dear Mike,

In message <200812090056.25498.vapier at gentoo.org> you wrote:
>
> > -: ${JOBS:=}
> > +# Determine number of CPU cores if no default was set
> > +: ${BUILD_NCPUS:"`getconf _NPROCESSORS_ONLN`"}
> > +
> > +if [ "$BUILD_NCPUS" -gt 1 ]
>
> no point in quoting here ... if it isnt numeric, then -gt will fail, and all
> numeric values lack whitespace ...

You are wrong. This is defensive programming against invalid user
input.

Assume the user runs

	BUILD_NCPUS=' ' MAKEALL

...

Without the quoting, we get a "[: -gt: unary operator expected" error
message; with the  quotes  we  single  process  build  as  (probably)
expected.

> > +then
> > +	JOBS-j`expr "$BUILD_NCPUS" + 1`
> > +else
> > +	JOBS""
> > +fi
>
> i generally see the heuristic (cpus * 2) rather than (cpus + 1) ... benchmarks
> tend to favor that as well ...

This obviously depends onyour  benchmarks.  For  U-Boot  builds,  all
systems  I've  checked  (with 512 MB or more of RAM) tend to have all
required files in RAM, so the only I/O is writing  the  object  files
and binaries out - which is negligable. In other words, the system is
nearly  100%  CPU  bound.  In  this  case,  (cpus  +  1)  seems  more
appropriate to me. But YMMV ...

Best regards,

Wolfgang Denk

-- 
DENX Software Engineering GmbH,     MD: Wolfgang Denk & Detlev Zundel
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at denx.de
 The software required `Windows 95 or better', so I installed Linux.