linux-kernel - Re: [RFC PATCH 00/14] Heterogeneous Memory System (HMS) and hbind()

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Message-Id: <d90b88f6-b414-a0f9-d572-35c4d2bb1579@linux.ibm.com>
Date:   Wed, 5 Dec 2018 16:57:17 +0530
From:   "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>
To:     Jerome Glisse <jglisse@...hat.com>,
        Dave Hansen <dave.hansen@...el.com>
Cc:     linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Matthew Wilcox <willy@...radead.org>,
        Ross Zwisler <ross.zwisler@...ux.intel.com>,
        Keith Busch <keith.busch@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Haggai Eran <haggaie@...lanox.com>,
        Balbir Singh <bsingharora@...il.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Felix Kuehling <felix.kuehling@....com>,
        Philip Yang <Philip.Yang@....com>,
        Christian König <christian.koenig@....com>,
        Paul Blinzer <Paul.Blinzer@....com>,
        Logan Gunthorpe <logang@...tatee.com>,
        John Hubbard <jhubbard@...dia.com>,
        Ralph Campbell <rcampbell@...dia.com>,
        Michal Hocko <mhocko@...nel.org>,
        Jonathan Cameron <jonathan.cameron@...wei.com>,
        Mark Hairgrove <mhairgrove@...dia.com>,
        Vivek Kini <vkini@...dia.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Dave Airlie <airlied@...hat.com>,
        Ben Skeggs <bskeggs@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Rik van Riel <riel@...riel.com>,
        Ben Woodard <woodard@...hat.com>, linux-acpi@...r.kernel.org
Subject: Re: [RFC PATCH 00/14] Heterogeneous Memory System (HMS) and hbind()

On 12/5/18 12:19 AM, Jerome Glisse wrote:

> Above example is for migrate. Here is an example for how the
> topology is use today:
> 
>      Application knows that the platform is running on have 16
>      GPU split into 2 group of 8 GPUs each. GPU in each group can
>      access each other memory with dedicated mesh links between
>      each others. Full speed no traffic bottleneck.
> 
>      Application splits its GPU computation in 2 so that each
>      partition runs on a group of interconnected GPU allowing
>      them to share the dataset.
> 
> With HMS:
>      Application can query the kernel to discover the topology of
>      system it is running on and use it to partition and balance
>      its workload accordingly. Same application should now be able
>      to run on new platform without having to adapt it to it.
> 

Will the kernel be ever involved in decision making here? Like the 
scheduler will we ever want to control how there computation units get 
scheduled onto GPU groups or GPU?

> This is kind of naive i expect topology to be hard to use but maybe
> it is just me being pesimistics. In any case today we have a chicken
> and egg problem. We do not have a standard way to expose topology so
> program that can leverage topology are only done for HPC where the
> platform is standard for few years. If we had a standard way to expose
> the topology then maybe we would see more program using it. At very
> least we could convert existing user.
> 
> 

I am wondering whether we should consider HMAT as a subset of the ideas
mentioned in this thread and see whether we can first achieve HMAT 
representation with your patch series?

-aneesh