lkml.org 
[lkml]   [2018]   [Sep]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: [PATCH net-next v6 07/23] zinc: ChaCha20 ARM and ARM64 implementations
Hey again Thomas,

On Thu, Sep 27, 2018 at 3:26 PM Jason A. Donenfeld <Jason@zx2c4.com> wrote:
>
> Hi Thomas,
>
> I'm trying to optimize this for crypto performance while still taking
> into account preemption concerns. I'm having a bit of trouble figuring
> out a way to determine numerically what the upper bounds for this
> stuff looks like. I'm sure I could pick a pretty sane number that's
> arguably okay -- and way under the limit -- but I still am interested
> in determining what that limit actually is. I was hoping there'd be a
> debugging option called, "warn if preemption is disabled for too
> long", or something, but I couldn't find anything like that. I'm also
> not quite sure what the latency limits are, to just compute this with
> a formula. Essentially what I'm trying to determine is:
>
> preempt_disable();
> asm volatile(".fill N, 1, 0x90;");
> preempt_enable();
>
> What is the maximum value of N for which the above is okay? What
> technique would you generally use in measuring this?
>
> Thanks,
> Jason

From talking to Peter (now CC'd) on IRC, it sounds like what you're
mostly interested in is clocktime latency on reasonable hardware, with
a goal of around ~20µs as a maximum upper bound? I don't expect to get
anywhere near this value at all, but if you can confirm that's a
decent ballpark, it would make for some interesting calculations.

Regards,
Jason

\
 
 \ /
  Last update: 2018-09-27 17:21    [W:0.132 / U:0.624 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site