Re: [PATCH v2 0/3] x86/fred: enable FRED by default

[Andy Lutomirski]

On Wed, Mar 25, 2026, at 4:01 PM, H. Peter Anvin wrote:
> From: H. Peter Anvin (Intel) <hpa@xxxxxxxxx>
>
> When FRED was added to the mainline kernel, it was set up as an
> explicit opt-in due to the risk of regressions before hardware was
> available publicly.
>
> Now, Panther Lake (Core Ultra 300 series) has been released, and
> benchmarking by Phoronix has shown that it provides a significant
> performance benefit on most workloads:
>
>     https://www.phoronix.com/review/intel-fred-panther-lake

Those performance increases while with fio / io_uring are ridiculous.  I wonder whether anyone can looked at /proc/interrupts to try to figure out what's going on.  I imagine we're bottlenecking on IO interrupts or something and FRED speeds that up by a factor of several, but this makes me wonder whether there's some tuning that should be done.

Jens, for background, FRED ought to speed up page faults and interrupts (both IPI and device) by a considerable amount -- maybe a reduction of 20k or more cycles per interrupt.  But Phoronix is showing up to a factor of 2 (!) actual performance increase using io_uring with a job count of 8.  Now maybe 8 is too small, but I'm wondering whether the io_uring or IO part is missing some optimization that it ought to have.

--Andy