[petsc-dev] slow "ar Scq" on cygwin

Matthew Knepley knepley at gmail.com
Thu Jun 28 15:34:48 CDT 2012

On Thu, Jun 28, 2012 at 2:23 PM, Chetan Jhurani <chetan.jhurani at gmail.com>wrote:

> Hi devs,
> Is there a way to avoid running the archiver (ar)
> every time a petsc directory is compiled?
> The reason I'm asking this is that when libpetsc.lib
> becomes large enough (say 100MB+, esp. for debug build),
> "ar Sqc" on cygwin takes very long in each directory.
> Depending on OS caching, very long can be 10 seconds per
> PETSc directory just to run ar.
> It creates a new temp file from scratch, puts stuff from
> libpetsc.lib and new stuff in it and then renames the
> temp file.  As you can imagine, the compilation process is
> fast in the beginning but crawls by the end.  I've seen
> the same IO sequence on Linux (with Sqc flags to ar), but
> since cygwin IO is slower the effect is more clearly visible.
> Building within a ramdisk leads to 25% faster compilation
> but it was more of a curiosity.

Build with Python. It never uses antique things like ar :)

  python2.7 ./config/builder2.py build


> Chetan

What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener
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