Michael Shell wrote:
On Mon, 24 Apr 2017 13:28:36 -0500
Bruce Dubbs <bruce.du...@gmail.com> wrote:
As for performance, I once did an automated build in a ramdisk. There
was no IO other than to RAM. The total speedup was 8% which is barely
noticeable if at all. LFS is CPU bound.
Bruce,
Not to suggest that your results are anything less than the perfect truth
of the reality of the matter, but I'm a bit surprised by this. Can I ask
what kind of hard drive you had - was it anything especially fast?
I don't recall when I did that test. It was not done on any of my current
systems. It was probably a 7200 RPM Seagate drive.
Right now I do builds on
Model Number: INTEL SSDSC2BP240G4
Model Number: WDC WD1003FBYX-01Y7B0
and do not notice a significant difference in build time in my logs. The
times do seem to increase with newer versions of software (e.g. binutils)
though.
Also, I think memory speed is a very important and grossly underrated
performance parameter. One could do a kernel compilation and compare
the results between various memory speed settings as a test. In fact,
I suspect that many online performance tests and benchmarks skew their
results (say to favor Intel over AMD, or whatever CPU they want to
show in a better light) by using a lower memory speed motherboard
setting with the "designated loser" than the actual RAM is rated for.
Most readers will focus on the CPU clock speed and will miss such a
difference.
I don't have a good reference for that. It would take some
experimentation. To me the biggest changes I notice are with newer
versions of Intel CPUs. Of course those also change the MB and RAM, so
it's hard to differentiate without direct experimentation. I'll leave
that to others. My rule of thumb though is that anything less than a 20%
improvement in build time is not noticeable except with instrumentation.
-- Bruce
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