linux-kernel - Re: [PATCH v4 0/5] powerpc/smp: Topology and shared processor optimizations

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Message-ID: <87v8a3zhl8.fsf@linux.ibm.com>
Date:   Wed, 15 Nov 2023 11:24:59 +0530
From:   "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>
To:     Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>
Cc:     Mark Rutland <mark.rutland@....com>,
        Valentin Schneider <vschneid@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org, Rohan McLure <rmclure@...ux.ibm.com>,
        Nicholas Piggin <npiggin@...il.com>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        Josh Poimboeuf <jpoimboe@...nel.org>
Subject: Re: [PATCH v4 0/5] powerpc/smp: Topology and shared processor
 optimizations

Srikar Dronamraju <srikar@...ux.vnet.ibm.com> writes:

> PowerVM systems configured in shared processors mode have some unique
> challenges. Some device-tree properties will be missing on a shared
> processor. Hence some sched domains may not make sense for shared processor
> systems.
>
> Most shared processor systems are over-provisioned. Underlying PowerVM
> Hypervisor would schedule at a Big Core granularity. The most recent power
> processors support two almost independent cores. In a lightly loaded
> condition, it helps the overall system performance if we pack to lesser
> number of Big Cores.
>

Is this good to do if the systems are not over-provisioned? What will be
the performance impact in that case with and without the change?

-aneesh