bug#40626: Poor performance on low-end ARMv7 devices

[Denis 'GNUtoo' Carikli]

On Mon, 13 Jul 2020 15:34:15 +0200
Ludovic Courtès <ludo@gnu.org> wrote:

> Hi,
> 
> Denis 'GNUtoo' Carikli <GNUtoo@cyberdimension.org> skribis:
> 
> > Many ARM Single Board Computers are commonly used with microSD for
> > storage, and some microSD cards are extremely slow (and sometimes
> > unreliable when they are old).
> >
> > Could the performance issues be related to storage device I/Os?
> 
> It could be the reason; it’s definitely the case on the board I was
> using here.
> 
> Still I wonder what could be done on our side to improve on this.
I guessed that was the intent.

A way to deal with that could be to validate if it's actually the case,
for instance by installing an SSD, and doing performance comparison
with the time command.

Then if it helps a lot, we probably need to trace the filesystem access
and optimize it somehow. Maybe that can be done with BPF or gprof, but
I never looked into obtimizing I/O performances, so I'm unsure if
that's the right approach. Guile may have profiling tools too.

As for benchmarking the CPU, I've patched phoronix-test-suite in a very
quick and dirty way in Parabola, so we could at least have some
benchmarks. For now we only have "compilation" benchmarks with source
code that should be FSDG compliant.

With it I've found that the compilation performances can vary a lot
between different ARM and x86 boards:
- An I.MX6 Quad with 2G of RAM is about 4.5x faster than the AM335x of a
  Beaglebone Green with 512M of RAM.
- A Lime2 A20 is about 1.7x faster than the Beaglebone Green and 2.5x
  slower than the board with the I.MX6 Quad.
- My smartphone (Galaxy SIII GT-I9300) is about 2x faster than my server
  (PC Engines APU1) for compilation.

Denis.

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