[RFC PATCH 0/5] running kernel mode SIMD with softirqs disabled

[Ard Biesheuvel]

On Sat, 19 Dec 2020 at 03:05, Herbert Xu <herbert at gondor.apana.org.au> wrote:
>
> On Fri, Dec 18, 2020 at 06:01:01PM +0100, Ard Biesheuvel wrote:
> >
> > Questions:
> > - what did I miss or break horribly?
> > - does any of this matter for RT? AIUI, RT runs softirqs from a dedicated
> >   kthread, so I don't think it cares.
> > - what would be a reasonable upper bound to keep softirqs disabled? I suppose
> >   100s of cycles or less is overkill, but I'm not sure how to derive a better
> >   answer.
> > - could we do the same on x86, now that kernel_fpu_begin/end is no longer
> >   expensive?
>
> If this approach works not only would it allow us to support the
> synchronous users better, it would also allow us to remove loads
> of cruft in the Crypto API that exist solely to support these SIMD
> code paths.
>
> So I eagerly await the assessment of the scheduler/RT folks on this
> approach.
>

Any insights here? Is there a ballpark upper bound for the duration of
a softirq disabled section? Other reasons why dis/enabling softirq
handling is a bad idea?