Message-ID: <34EF90DF7C7F0647A403B771519912C7F5382CF3@irsmsx111.ger.corp.intel.com>
Date:   Fri, 22 Dec 2017 10:31:05 +0000
From:   "Kogut, Jaroslaw" <Jaroslaw.Kogut@...el.com>
To:     Anshuman Khandual <khandual@...ux.vnet.ibm.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Ross Zwisler <ross.zwisler@...ux.intel.com>
CC:     "Anaczkowski, Lukasz" <lukasz.anaczkowski@...el.com>,
        "Box, David E" <david.e.box@...el.com>,
        "Koss, Marcin" <marcin.koss@...el.com>,
        "Koziej, Artur" <artur.koziej@...el.com>,
        "Lahtinen, Joonas" <joonas.lahtinen@...el.com>,
        "Moore, Robert" <robert.moore@...el.com>,
        "Nachimuthu, Murugasamy" <murugasamy.nachimuthu@...el.com>,
        "Odzioba, Lukasz" <lukasz.odzioba@...el.com>,
        "Wysocki, Rafael J" <rafael.j.wysocki@...el.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        "Schmauss, Erik" <erik.schmauss@...el.com>,
        "Verma, Vishal L" <vishal.l.verma@...el.com>,
        "Zheng, Lv" <lv.zheng@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Balbir Singh <bsingharora@...il.com>,
        Brice Goglin <brice.goglin@...il.com>,
        "Williams, Dan J" <dan.j.williams@...el.com>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        Jerome Glisse <jglisse@...hat.com>,
        John Hubbard <jhubbard@...dia.com>,
        Len Brown <lenb@...nel.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        "devel@...ica.org" <devel@...ica.org>,
        "linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>
Subject: RE: [PATCH v3 0/3] create sysfs representation of ACPI HMAT

> ... first thinking about redesigning the NUMA for
> heterogeneous memory may not be a good idea. Will look into this further.

I agree with comment that first a direction should be defined how to handle heterogeneous memory system.

> https://linuxplumbersconf.org/2017/ocw//system/presentations/4656/original/
> Hierarchical_NUMA_Design_Plumbers_2017.pdf

I miss in the presentation a user perspective of the new approach, e.g.
- How does application developer see/understand the heterogeneous memory system?
- How does app developer use the heterogeneous memory system? 
- What are modification in API/sys interfaces?

In other hand, if we assume that separate memory NUMA node has different memory capabilities/attributes from stand point of particular CPU, it is easy to explain for user how to describe/handle heterogeneous memory. 

Of course, current numa design is not sufficient in kernel in following areas today:
- Exposing memory attributes that describe heterogeneous memory system
- Interfaces to use the heterogeneous memory system, e.g. more sophisticated policies
- Internal mechanism in memory management, e.g. automigration, maybe something else.

> -----Original Message-----
> From: Anshuman Khandual [mailto:khandual@...ux.vnet.ibm.com]
> Sent: Friday, December 22, 2017 4:10 AM
> To: Ross Zwisler <ross.zwisler@...ux.intel.com>; linux-kernel@...r.kernel.org
> Cc: Anaczkowski, Lukasz <lukasz.anaczkowski@...el.com>; Box, David E
> <david.e.box@...el.com>; Kogut, Jaroslaw <Jaroslaw.Kogut@...el.com>; Koss,
> Marcin <marcin.koss@...el.com>; Koziej, Artur <artur.koziej@...el.com>;
> Lahtinen, Joonas <joonas.lahtinen@...el.com>; Moore, Robert
> <robert.moore@...el.com>; Nachimuthu, Murugasamy
> <murugasamy.nachimuthu@...el.com>; Odzioba, Lukasz
> <lukasz.odzioba@...el.com>; Wysocki, Rafael J <rafael.j.wysocki@...el.com>;
> Rafael J. Wysocki <rjw@...ysocki.net>; Schmauss, Erik
> <erik.schmauss@...el.com>; Verma, Vishal L <vishal.l.verma@...el.com>;
> Zheng, Lv <lv.zheng@...el.com>; Andrew Morton <akpm@...ux-
> foundation.org>; Balbir Singh <bsingharora@...il.com>; Brice Goglin
> <brice.goglin@...il.com>; Williams, Dan J <dan.j.williams@...el.com>;
> Hansen, Dave <dave.hansen@...el.com>; Jerome Glisse <jglisse@...hat.com>;
> John Hubbard <jhubbard@...dia.com>; Len Brown <lenb@...nel.org>; Tim
> Chen <tim.c.chen@...ux.intel.com>; devel@...ica.org; linux-
> acpi@...r.kernel.org; linux-mm@...ck.org; linux-nvdimm@...ts.01.org
> Subject: Re: [PATCH v3 0/3] create sysfs representation of ACPI HMAT
> 
> On 12/14/2017 07:40 AM, Ross Zwisler wrote:
> > ==== Quick Summary ====
> >
> > Platforms exist today which have multiple types of memory attached to
> > a single CPU.  These disparate memory ranges have some characteristics
> > in common, such as CPU cache coherence, but they can have wide ranges
> > of performance both in terms of latency and bandwidth.
> 
> Right.
> 
> >
> > For example, consider a system that contains persistent memory,
> > standard DDR memory and High Bandwidth Memory (HBM), all attached to
> the same CPU.
> > There could potentially be an order of magnitude or more difference in
> > performance between the slowest and fastest memory attached to that CPU.
> 
> Right.
> 
> >
> > With the current Linux code NUMA nodes are CPU-centric, so all the
> > memory attached to a given CPU will be lumped into the same NUMA node.
> > This makes it very difficult for userspace applications to understand
> > the performance of different memory ranges on a given CPU.
> 
> Right but that might require fundamental changes to the NUMA
> representation.
> Plugging those memory as separate NUMA nodes, identify them through sysfs
> and try allocating from it through mbind() seems like a short term solution.
> 
> Though if we decide to go in this direction, sysfs interface or something similar
> is required to enumerate memory properties.
> 
> >
> > We solve this issue by providing userspace with performance
> > information on individual memory ranges.  This performance information
> > is exposed via
> > sysfs:
> >
> >   # grep . mem_tgt2/* mem_tgt2/local_init/* 2>/dev/null
> >   mem_tgt2/firmware_id:1
> >   mem_tgt2/is_cached:0
> >   mem_tgt2/local_init/read_bw_MBps:40960
> >   mem_tgt2/local_init/read_lat_nsec:50
> >   mem_tgt2/local_init/write_bw_MBps:40960
> >   mem_tgt2/local_init/write_lat_nsec:50
> 
> I might have missed discussions from earlier versions, why we have this kind of
> a "source --> target" model ? We will enlist properties for all possible "source --
> > target" on the system ? Right now it shows only bandwidth and latency
> properties, can it accommodate other properties as well in future ?
> 
> >
> > This allows applications to easily find the memory that they want to use.
> > We expect that the existing NUMA APIs will be enhanced to use this new
> > information so that applications can continue to use them to select
> > their desired memory.
> 
> I had presented a proposal for NUMA redesign in the Plumbers Conference this
> year where various memory devices with different kind of memory attributes
> can be represented in the kernel and be used explicitly from the user space.
> Here is the link to the proposal if you feel interested. The proposal is very
> intrusive and also I dont have a RFC for it yet for discussion here.
> 
> https://linuxplumbersconf.org/2017/ocw//system/presentations/4656/original/
> Hierarchical_NUMA_Design_Plumbers_2017.pdf
> 
> Problem is, designing the sysfs interface for memory attribute detection from
> user space without first thinking about redesigning the NUMA for
> heterogeneous memory may not be a good idea. Will look into this further.

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