From: Nick Kossifidis <mick@ics.forth.gr>
To: Palmer Dabbelt <palmer@sifive.com>
Cc: robh+dt@kernel.org, mark.rutland@arm.com,
devicetree@vger.kernel.org, Damien.LeMoal@wdc.com,
alankao@andestech.com, zong@andestech.com, anup@brainfault.org,
linux-kernel@vger.kernel.org,
Christoph Hellwig <hch@infradead.org>,
atish.patra@wdc.com, linux-riscv@lists.infradead.org,
tglx@linutronix.de
Subject: Re: [RFC 1/2] dt-bindings: topology: Add RISC-V cpu topology.
Date: Tue, 06 Nov 2018 12:03:17 +0200 [thread overview]
Message-ID: <9e77989d6b868d914bc328401cd64557@mailhost.ics.forth.gr> (raw)
In-Reply-To: <mhng-799bd6f4-e4af-481e-90d8-bdc0e30f2530@palmer-si-x1c4>
Στις 2018-11-05 21:38, Palmer Dabbelt έγραψε:
> On Fri, 02 Nov 2018 06:09:39 PDT (-0700), robh+dt@kernel.org wrote:
>> On Thu, Nov 1, 2018 at 6:04 PM Atish Patra <atish.patra@wdc.com>
>> wrote:
>>>
>>> Define a RISC-V cpu topology. This is based on cpu-map in ARM world.
>>> But it doesn't need a separate thread node for defining SMT systems.
>>> Multiple cpu phandle properties can be parsed to identify the sibling
>>> hardware threads. Moreover, we do not have cluster concept in RISC-V.
>>> So package is a better word choice than cluster for RISC-V.
>>
>> There was a proposal to add package info for ARM recently. Not sure
>> what happened to that, but we don't need 2 different ways.
>>
>> There's never going to be clusters for RISC-V? What prevents that?
>> Seems shortsighted to me.
>>
>>>
>>> Signed-off-by: Atish Patra <atish.patra@wdc.com>
>>> ---
>>> .../devicetree/bindings/riscv/topology.txt | 154
>>> +++++++++++++++++++++
>>> 1 file changed, 154 insertions(+)
>>> create mode 100644
>>> Documentation/devicetree/bindings/riscv/topology.txt
>>>
>>> diff --git a/Documentation/devicetree/bindings/riscv/topology.txt
>>> b/Documentation/devicetree/bindings/riscv/topology.txt
>>> new file mode 100644
>>> index 00000000..96039ed3
>>> --- /dev/null
>>> +++ b/Documentation/devicetree/bindings/riscv/topology.txt
>>> @@ -0,0 +1,154 @@
>>> +===========================================
>>> +RISC-V cpu topology binding description
>>> +===========================================
>>> +
>>> +===========================================
>>> +1 - Introduction
>>> +===========================================
>>> +
>>> +In a RISC-V system, the hierarchy of CPUs can be defined through
>>> following nodes that
>>> +are used to describe the layout of physical CPUs in the system:
>>> +
>>> +- packages
>>> +- core
>>> +
>>> +The cpu nodes (bindings defined in [1]) represent the devices that
>>> +correspond to physical CPUs and are to be mapped to the hierarchy
>>> levels.
>>> +Simultaneous multi-threading (SMT) systems can also represent their
>>> topology
>>> +by defining multiple cpu phandles inside core node. The details are
>>> explained
>>> +in paragraph 3.
>>
>> I don't see a reason to do this differently than ARM. That said, I
>> don't think the thread part is in use on ARM, so it could possibly be
>> changed.
>>
>>> +
>>> +The remainder of this document provides the topology bindings for
>>> ARM, based
>>
>> for ARM?
>>
>>> +on the Devicetree Specification, available from:
>>> +
>>> +https://www.devicetree.org/specifications/
>>> +
>>> +If not stated otherwise, whenever a reference to a cpu node phandle
>>> is made its
>>> +value must point to a cpu node compliant with the cpu node bindings
>>> as
>>> +documented in [1].
>>> +A topology description containing phandles to cpu nodes that are not
>>> compliant
>>> +with bindings standardized in [1] is therefore considered invalid.
>>> +
>>> +This cpu topology binding description is mostly based on the
>>> topology defined
>>> +in ARM [2].
>>> +===========================================
>>> +2 - cpu-topology node
>>
>> cpu-map. Why change this?
>>
>> What I would like to see is the ARM topology binding reworked to be
>> common or some good reasons why it doesn't work for RISC-V as-is.
>
> I think it would be great if CPU topologies were not a RISC-V specific
> thing. We don't really do anything different than anyone else, so
> it'd be great if we could all share the same spec and code. Looking
> quickly at the ARM cpu-map bindings, I don't see any reason why we
> can't just use the same thing on RISC-V -- it's not quite how I'd do
> it, but I don't think the differences are worth having another
> implementation. Mechanically I'm not sure how to do this: should
> there just be a "Documentation/devicetree/bindings/cpu-map.txt"?
>
> If everyone is OK with that then I vote we just go ahead and
> genericise the ARM "cpu-map" stuff for CPU topology. Sharing the
> implementation looks fairly straight-forward as well.
>
Please check this out...
https://lkml.org/lkml/2018/11/3/99
It's also non arch-dependent and it can handle the scheduler's
capabilities
better than cpu-map.
next prev parent reply other threads:[~2018-11-06 10:05 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-01 23:04 [RFC 0/2] Add RISC-V cpu topology Atish Patra
2018-11-01 23:04 ` [RFC 1/2] dt-bindings: topology: " Atish Patra
2018-11-02 13:09 ` Rob Herring
2018-11-02 13:31 ` Sudeep Holla
2018-11-02 15:11 ` Rob Herring
2018-11-02 15:50 ` Sudeep Holla
2018-11-02 20:53 ` Atish Patra
2018-11-02 21:08 ` Rob Herring
2018-11-02 20:34 ` Atish Patra
2018-11-05 19:38 ` Palmer Dabbelt
2018-11-05 20:10 ` Rob Herring
2018-11-06 0:12 ` Atish Patra
2018-11-06 10:03 ` Nick Kossifidis [this message]
2018-11-06 11:37 ` Mark Rutland
2018-11-01 23:04 ` [RFC 2/2] RISC-V: Introduce " Atish Patra
2018-11-02 18:58 ` [RFC 0/2] Add RISC-V " Nick Kossifidis
2018-11-02 21:14 ` Atish Patra
2018-11-02 22:18 ` Nick Kossifidis
2018-11-06 14:13 ` Sudeep Holla
2018-11-06 15:26 ` Nick Kossifidis
2018-11-06 15:50 ` Sudeep Holla
2018-11-06 16:20 ` Mark Rutland
2018-11-07 2:31 ` Nick Kossifidis
2018-11-07 12:06 ` Mark Rutland
2018-11-08 13:45 ` Nick Kossifidis
2018-11-08 15:54 ` Mark Rutland
2018-11-09 3:55 ` Nick Kossifidis
2018-11-07 12:28 ` Sudeep Holla
2018-11-08 14:52 ` Nick Kossifidis
2018-11-08 16:48 ` Sudeep Holla
2018-11-09 2:36 ` Nick Kossifidis
2018-11-09 12:33 ` Sudeep Holla
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