Subject: Re: [PATCH V2] powerpc/irq: Enable some more exceptions in /proc/interrupts interface

From: Michael Ellerman <[email-masked]>
Date: Mon, 13 Jul 2015 15:41:16 +1000

On Mon, 2015-07-13 at 10:54 +0530, Anshuman Khandual wrote:
> On 07/10/2015 12:40 PM, Michael Neuling wrote:
> > What's the performance impact of this?  If you run this test with --fp,
> > --altivec or --vector what is the impact of adding this patch?
> > 
> > http://ozlabs.org/~anton/junkcode/context_switch2.c
> > 
> > eg 
> >   ./context_switch2 --fp 0 0 
> 
> Please find the results here which looks similar with or without
> the patch being applied.

No they don't look similar with or without.

> (A) Floating point context switches (context_switch2 --fp 0 0)

If you just sort them you see:

316478	after
316540	after
316650	after
318448	after
318904 before
320216 before
321206 before
321308 before
323460	after
324596 before

It looks like ~1% degradation. Please run the test more times (maybe 1000) and
see how the numbers look.

cheers