Re: [LSF/MM/BPF TOPIC] Measuring limits and enhancing buffered IO

Linus Torvalds
2024-02-27T16:35:02Z

On Mon, 26 Feb 2024 at 23:22, Kent Overstreet <kent.overstreet@linux.dev> wrote:
>
> Only rough testing, but this is looking like around a 25% performance
> increase doing 4k random reads on a 1G file with fio, 8 jobs, on my
> Ryzen 5950x - 16.7M -> 21.4M iops, very roughly. fio's a pig and we're
> only spending half our cpu time in the kernel, so the buffered read path
> is actually getting 40% or 50% faster.
>
> So I'd say that's substantial.

No, you're doing something wrong. The new fastread logic only
triggers for reads <= 128 bytes, so you must have done some other
major change (like built a kernel without the mitigations, and
compared it to one with mitigations - that would easily be 25%
depending on hardware).

Linus