linux-kernel - Re: [PATCH v4 1/5] powerpc/smp: Enable Asym packing for cores on shared processor

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Date:   Wed, 15 Nov 2023 10:57:08 +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>,
        Nicholas Piggin <npiggin@...il.com>,
        Christophe Leroy <christophe.leroy@...roup.eu>
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>,
        "ndesaulniers@...gle.com" <ndesaulniers@...gle.com>,
        linux-kernel@...r.kernel.org, Rohan McLure <rmclure@...ux.ibm.com>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        Josh Poimboeuf <jpoimboe@...nel.org>
Subject: Re: [PATCH v4 1/5] powerpc/smp: Enable Asym packing for cores on
 shared processor

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

> If there are shared processor LPARs, underlying Hypervisor can have more
> virtual cores to handle than actual physical cores.
>
> Starting with Power 9, a big core (aka SMT8 core) has 2 nearly
> independent thread groups. On a shared processors LPARs, it helps to
> pack threads to lesser number of cores so that the overall system
> performance and utilization improves. PowerVM schedules at a big core
> level. Hence packing to fewer cores helps.
>
> For example: Lets says there are two 8-core Shared LPARs that are
> actually sharing a 8 Core shared physical pool, each running 8 threads
> each. Then Consolidating 8 threads to 4 cores on each LPAR would help
> them to perform better. This is because each of the LPAR will get
> 100% time to run applications and there will no switching required by
> the Hypervisor.
>

Will this patch consolidate things to first 8 threads or just the one
Big core? /me continues to look at other patches and wonder whether 4/5
should come before this? 


>
> To achieve this, enable SD_ASYM_PACKING flag at CACHE, MC and DIE level
> when the system is running in shared processor mode and has big cores.
>
> Signed-off-by: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>


-aneesh