Re: [PATCH v3 0/9] Introduce SMT level and add PowerPC support

[Laurent Dufour]

Le 30/06/2023 à 15:32, Sachin Sant a écrit :
> > On 29-Jun-2023, at 8:01 PM, Laurent Dufour <ldufour@xxxxxxxxxxxxx> wrote:
> >
> > I'm taking over the series Michael sent previously [1] which is smartly
> > reviewing the initial series I sent [2].  This series is addressing the
> > comments sent by Thomas and me on the Michael's one.
> >
> > Here is a short introduction to the issue this series is addressing:
> >
> > When a new CPU is added, the kernel is activating all its threads. This
> > leads to weird, but functional, result when adding CPU on a SMT 4 system
> > for instance.
> >
> > Here the newly added CPU 1 has 8 threads while the other one has 4 threads
> > active (system has been booted with the 'smt-enabled=4' kernel option):
> >
> > ltcden3-lp12:~ # ppc64_cpu --info
> > Core   0:    0*    1*    2*    3*    4     5     6     7
> > Core   1:    8*    9*   10*   11*   12*   13*   14*   15*
> >
> > This mixed SMT level may confused end users and/or some applications.
> >
> > There is no SMT level recorded in the kernel (common code), neither in user
> > space, as far as I know. Such a level is helpful when adding new CPU or
> > when optimizing the energy efficiency (when reactivating CPUs).
> >
> > When SMP and HOTPLUG_SMT are defined, this series is adding a new SMT level
> > (cpu_smt_num_threads) and few callbacks allowing the architecture code to
> > fine control this value, setting a max and a "at boot" level, and
> > controling whether a thread should be onlined or not.
> >
> > v3:
> >   Fix a build error in the patch 6/9
>
> Successfully tested the V3 version on a Power10 LPAR. Add/remove of
> processor core worked correctly, preserving the SMT level (on a kernel
> booted with smt-enabled= parameter)
>
> Laurent (Thanks!) also provided a patch to update the ppc64_cpu &
> lparstat utility. With patched ppc64_cpu utility verified that SMT level
> changed at runtime was preserved across processor core add (on
> a kernel booted without smt-enabled= parameter)
>
> Based on these test results
>
> Tested-by: Sachin Sant <sachinp@xxxxxxxxxxxxx>

Thanks a lot, Sachin!

Once this series is accepted, I'll send the series to update ppc64_cpu.