Re: [PATCH v4 1/1] powerpc: enable dynamic preemption

[Jirka Hladky]

On Fri, Jul 31, 2026 at 7:03 AM Christophe Leroy (CS GROUP)
<chleroy@xxxxxxxxxx> wrote:
>
>
>
> Le 30/07/2026 à 19:10, Shrikanth Hegde a écrit :
> > Hi Jirka, Paul,
> >
> >
> > +cc will
> >
> > On 7/30/26 8:38 PM, Jirka Hladky wrote:
> >> On Thu, Jul 30, 2026 at 4:53 PM Paul E. McKenney <paulmck@xxxxxxxxxx>
> >> wrote:
> >>> But is this really a fundamental RISC cost?  For example, does arm64
> >>> see the same performance issues?
> >>
> >> We tested arm64 (Ampere Altra Max) with the same controlled
> >> experiment -- two 6.18 kernels, both voluntary, differing only in
> >> PREEMPT_DYNAMIC:
> >>
> >> Arch     PREEMPT_DYNAMIC   kill bogo-ops/sec   Delta
> >> -------  ---------------   -----------------   -----
> >> ppc64le  off               108,836
> >> ppc64le  on                 68,197             -37.3%
> >> aarch64  off                 5,538
> >> aarch64  on                  5,082              -8.2%
> >>
> >> arm64 sees -8.2% vs ppc64le's -37.3%. So arm64 is affected but
> >> much less severely.
> >
> > Ouch!. But that's good to know.
>
> Might be a stupid question, but what is your .config ?
> Are you sure it doesn't contain CONFIG_DEBUG_PREEMPT ?

I have double-checked that and it's not set:
# CONFIG_DEBUG_PREEMPT is not set

Thanks
Jirka