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

[Andreas Hindborg <a.hindborg@kernel.org>]

"Niklas Cassel" <cassel@kernel.org> writes:

> 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 ?

Yes.

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

Yes, I did not do that. I should collect some more detailed data for
past kernels.

> 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.
>

I'll try that, thanks.


Best regards,
Andreas Hindborg