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

Chetan Jhurani chetan.jhurani at gmail.com
Thu Jun 28 15:23:11 CDT 2012

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.


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