Re: Parallel builds across makefiles

[David Boyce]

A couple of suggestions:

1. Check your value of TMPDIR if any. All -O is doing is redirecting output into a temp file and dumping it later. Effectively it turns command "foo" into "foo > $TMPDIR/blah; cat $TMPDIR/blah; unlink $TMPDIR/blah". This is why it seems almost impossible for it to slow things down appreciably, and a slow temp dir device might be one explanation. Along similar lines you could try "TMPDIR=/tmp make ..."

2. Try strace. It has a mode which will timestamp each system call and another which prints a table of system calls used and how much time it took. One of these will probably be instructive, especially when compared with the same without -O.

David

On Sun, Jul 17, 2016 at 12:22 PM, Gardell, Steven <address@hidden> wrote:

No I have not gotten to 4.2.1 yet.

I have experimented using j values ranging from 16 to 64. The majority of the testing is with -Otarget. But I have tried all of them.

-----Original Message-----
From: Paul Smith [mailto:address@hidden]
Sent: Sunday, July 17, 2016 3:14 PM
To: Gardell, Steven <address@hidden>; address@hidden
Subject: Re: Parallel builds across makefiles

On Sun, 2016-07-17 at 15:48 +0000, Gardell, Steven wrote:
> OK. Thanks! I will try the latest version.
>
> FWIW, I am measuring is total wall clock time to complete the build.
> (date; gmake... ; date) This goes up substantially with all sync modes
> other than "none" if gmake has parallel invocations of sub-makes going
> (e.g. "gmake  -f SomeOtherMakefile").  When I am only parallelizing
> individual makefiles (with ACE, these tend to be simple lists of files
> to compile), then the behavior is as promised by the documentation.

Assuming you determine the behavior exists even in version 4.2.1, please provide more details.  What level of -j are you using?  Which sync mode are you using?  Do you get the same behavior even with lower levels of -j, if yours is very large?

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