linux-kernel - Re: [PATCH 3/3] powerpc/cacheinfo: Print correct cache-sibling map/list for L2 cache

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Message-ID: <20201209090709.GB13125@in.ibm.com>
Date:   Wed, 9 Dec 2020 14:37:09 +0530
From:   Gautham R Shenoy <ego@...ux.vnet.ibm.com>
To:     Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:     Gautham R Shenoy <ego@...ux.vnet.ibm.com>,
        Anton Blanchard <anton@...abs.org>,
        Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Michael Neuling <mikey@...ling.org>,
        Nicholas Piggin <npiggin@...il.com>,
        Nathan Lynch <nathanl@...ux.ibm.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Valentin Schneider <valentin.schneider@....com>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] powerpc/cacheinfo: Print correct cache-sibling
 map/list for L2 cache

On Wed, Dec 09, 2020 at 02:09:21PM +0530, Srikar Dronamraju wrote:
> * Gautham R Shenoy <ego@...ux.vnet.ibm.com> [2020-12-08 23:26:47]:
> 
> > > The drawback of this is even if cpus 0,2,4,6 are released L1 cache will not
> > > be released. Is this as expected?
> > 
> > cacheinfo populates the cache->shared_cpu_map on the basis of which
> > CPUs share the common device-tree node for a particular cache.  There
> > is one l1-cache object in the device-tree for a CPU node corresponding
> > to a big-core. That the L1 is further split between the threads of the
> > core is shown using ibm,thread-groups.
> > 
> 
> Yes.
> 
> > The ideal thing would be to add a "group_leader" field to "struct
> > cache" so that we can create separate cache objects , one per thread
> > group. I will take a stab at this in the v2.
> > 
> 
> I am not saying this needs to be done immediately. We could add a TODO and
> get it done later. Your patch is not making it worse. Its just that there is
> still something more left to be done.

Yeah, it needs to be fixed but it may not be a 5.11 target. For now I
will fix this patch to take care of the build errors on !PPC64 !SMT
configs. I will post a separate series for making cacheinfo.c aware of
thread-groups at the time of construction of the cache-chain.

> 
> -- 
> Thanks and Regards
> Srikar Dronamraju