Re: measuring swap partition speed

void <void_at_f-m.fm> wrote on
Date: Fri, 22 Dec 2023 16:59:10 UTC :

> My assessment of the "system being inactive while testing" may have
> been inaccurate. By "being inactive" I was looking at avg load being
> 1% or less, and for swap use being 0. Maybe the initial "inactive" test 
> should have been in single user mode [1] because the tests in this mode
> show no (I mean much less) of a speed issue. Apologies for not considering 
> single user mode till now. The results in single user mode seem to me to 
> infer that there is no problem with the hardware.

Suggestion: Compare/contrast what you see via "gstat -spod" for single
user vs. not when you are not deliberately running the swap I/O
test but other things are similar to when you do.

> I have been able to reliably create the problem by rebooting the
> computer, then running something that does not need to be one huge chunk of data,
> that doesn't load the system that much, so ran 'make installworld' and in another 
> terminal ran the write-to-swap-partition test [2].

I suggest monitoring what "gstat -spod" shows during a make installworld
run (no competing writes to swap). Then with both going in overlapping
time frames: what is noticably different?

I wonder if UFS vs. ZFS contributes for the RAM-related bandwidth limited
RPi4B. (One core can saturate the RAM-related subsystem depending on
how effective the RAM caching happens to be for the access patterns
involved.)

> It shows in this context 
> that writing to the filesystem effectively blocks writing to swap. 
> 507 kB/s compared to 16 MB/s. I don't know if this is unique to arm64 or 
> if it's also the case on other arches, but it seems suboptimal to me.

I do not have a built world to install on my stable/14 snapshot
media. I'll have to switch to a main [so: 15] media (that is not
up to date) if I'm going to provide some sort of matching type
of activity comparison/contrast. This would be using a newer
USB3 NVMe media. Probably UFS instead of ZFS instead: I may not
have both of the main [so: 15] media available to me for now.

If I do this, it will likely not be quickly.

===
Mark Millard
marklmi at yahoo.com