Re: [Lsf-pc] [LSF/MM/BPF TOPIC] Rust block layer abstractions and benchmark strategies

[Niklas Cassel <cassel@kernel.org>]

Hello Andreas,

On Tue, Jan 21, 2025 at 01:51:11PM +0100, Andreas Hindborg wrote:
> Hi Jan,
> 
> "Jan Kara" <jack@suse.cz> writes:
> 
> > Hi!
> >
> > On Tue 21-01-25 12:13:48, Andreas Hindborg via Lsf-pc wrote:
> >> I would like to propose that we have a session on Rust in the block
> >> layer again this year. Specifically I would like to discuss some rather
> >> puzzling results I observe when I benchmark the C and Rust null block
> >> drivers. I did a write up of the challenges I face at [1]. The
> >> observations are not tied to rust, they also manifest in the C driver.
> >
> > The results are indeed somewhat curious. One factor I didn't see addressed
> > in your blog is CPU scheduling. I've seen in the past cases where IO tasks
> > were getting migrated across cores leading to jumps in perfomance. Did you
> > try binding fio jobs to one CPU each?
> 
> Yes, I am pinning the io jobs to cores with fio options `cpus_allowed=0-<jobs>`
> and `--cpus_allowed_policy=split` so I get 1 job per core.
> 
> The kernel is configured with PREEMPT_NONE=y.

"I also cover a problem with the benchmark results that manifested during
testing for v6.12-rc2."

I assume that all the results on:
https://metaspace.github.io/2024/12/02/problems-in-benchmark-land.html

are with kernel v6.12-rc2 ?

It would be interesting to test an older kernel version, and see if it
is e.g. a scheduler bug.


You might also want to test with this series applied (which landed last
minute before v6.13 was tagged):
https://lore.kernel.org/lkml/20250119110410.GAZ4zcKkx5sCjD5XvH@fat_crate.local/T/#u


It fixes bugs that were introduced in v6.12-rc1 and v6.7-rc2 respectively.


Kind regards,
Niklas