On Sun, May 10, 2020 at 9:47 PM David Laight <david.lai...@aculab.com> wrote: > > From: Joe Perches > > Sent: 08 May 2020 16:06 > > On Fri, 2020-05-08 at 13:49 +0200, Arnd Bergmann wrote: > > > Personally, I'm more interested in improving compile speed of the kernel > > > > Any opinion on precompiled header support? > > When ever I've been anywhere near it it is always a disaster. > It may make sense for C++ where there is lots of complicated > code to parse in .h files. Parsing C headers is usually easier. > > One this I have done that significantly speeds up .h file > processing is to take the long list of '-I directory' parameters > that are passed to the compiler and copy the first version > of each file into a separate 'object headers' directory. > This saves the compiler doing lots of 'failed opens'. > > If each fragment makefile lists its 'public' headers make > can generate dependency rules that do the copies. > > FWIW make is much faster if you delete all the builtin and > suffix rules and rely on explicit rules for each file.
Kbuild disables Make's builtin rules at least. # Do not use make's built-in rules and variables # (this increases performance and avoids hard-to-debug behaviour) MAKEFLAGS += -rR -- Best Regards Masahiro Yamada
