RPI3 swap experiments

[bob prohaska]

On Mon, Jul 23, 2018 at 12:11:19AM -0700, Mark Millard wrote:
> 
> 
> On 2018-Jul-22, at 11:35 PM, bob prohaska <fbsd at www.zefox.net> wrote:
> 
> >> . . .
> > There is some reason to think "newer" Sandisk Extreme devices differ, perhaps
> > in a bad way, from older devices. The older device in my tests is model
> > SDCZ80-064G and is simply labeled USB3.0. The newer, troublesome device
> > is model SDCZ800-064G and is labeled Extreme Go USB 3.1. There are reports
> > that the Extreme Go is slower, advising to buy the older devices if possible.
> > 
> > The USB3.1 flash drive is back in test, with the results of a j4 buildworld
> > under r336567 at
> > http://www.zefox.net/~fbsd/rpi3/swaptests/r336567/
> > 
> > The worst case results are still fairly dismal, close to a minute. All the
> > swap was on microSD, so OOMA didn't strike and buildworld completed successfully.
> > Near as I can tell no errors were reported on the console.
> 
> 
> Rebuilds that do not rebuild the llvm materials (clang, lld, lldb, etc.) are not all that
> comparable to ones that do. (This is visible in the time differences in the builds that
> complete.) The llvm related build activity likely involves most of the potential
> swapping, for example. Also: lots of I/O.
> 
> There can be two rebuilds of some of the llvm material. One stage with such is the
> cross-compiler:
> --- buildworld ---
> make[1]: "/usr/src/Makefile.inc1" line 341: SYSTEM_COMPILER: Determined that CC=cc matches the source tree.  Not bootstrapping a cross-compiler.
> make[1]: "/usr/src/Makefile.inc1" line 346: SYSTEM_LINKER: Determined that LD=ld matches the source tree.  Not bootstrapping a cross-linker.
> (it was not rebuilt in the example). The other involves the build of the system llvm materials for
> use in the (potentially) installed system, such as the system's clang.
> 
> Taking an environment that worked for lack of llvm related rebuilds may not
> well indicate the result for rebuilds that would try to rebuild the llvm related
> materials.
> 
> It is something to consider in what builds are compared, how they are
> compared, and what one infers from comparisons.
> 

The first step in the experiment is to run a cleanup script, consisting of

make -j8 cleandir > cleandir.log && make -j8 cleandir > cleandir.log && rm -rf /usr/obj/usr/src && rm *.log

Might this be insufficient to ensure a clean start? There's no obvious reason to build
a cross compiler, since this is an RPI3 building world for itself. Is there an error in the 
cleanup script?

Thanks for reading!

bob prohaska