From: Jonathan Cameron <Jonathan.Cameron@Huawei.com>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: <linux-acpi@vger.kernel.org>,
<linux-arm-kernel@lists.infradead.org>,
<linux-kernel@vger.kernel.org>, <x86@kernel.org>,
Len Brown <len.brown@intel.com>,
Sudeep Holla <sudeep.holla@arm.com>, <guohanjun@huawei.com>,
Will Deacon <will@kernel.org>, <linuxarm@huawei.com>,
Brice Goglin <Brice.Goglin@inria.fr>
Subject: Re: [RFC PATCH] topology: Represent clusters of CPUs within a die.
Date: Mon, 19 Oct 2020 09:08:54 +0100 [thread overview]
Message-ID: <20201019080854.00001a9f@Huawei.com> (raw)
In-Reply-To: <20201017064425.GB1883987@kroah.com>
On Sat, 17 Oct 2020 08:44:25 +0200
Greg Kroah-Hartman <gregkh@linuxfoundation.org> wrote:
> On Fri, Oct 16, 2020 at 11:27:02PM +0800, Jonathan Cameron wrote:
> > Both ACPI and DT provide the ability to describe additional layers of
> > topology between that of individual cores and higher level constructs
> > such as the level at which the last level cache is shared.
> > In ACPI this can be represented in PPTT as a Processor Hierarchy
> > Node Structure [1] that is the parent of the CPU cores and in turn
> > has a parent Processor Hierarchy Nodes Structure representing
> > a higher level of topology.
> >
> > For example Kunpeng 920 has clusters of 4 CPUs. These do not share
> > any cache resources, but the interconnect topology is such that
> > the cost to transfer ownership of a cacheline between CPUs within
> > a cluster is lower than between CPUs in different clusters on the same
> > die. Hence, it can make sense to deliberately schedule threads
> > sharing data to a single cluster.
> >
> > This patch simply exposes this information to userspace libraries
> > like hwloc by providing cluster_cpus and related sysfs attributes.
> > PoC of HWLOC support at [2].
> >
> > Note this patch only handle the ACPI case.
> >
> > Special consideration is needed for SMT processors, where it is
> > necessary to move 2 levels up the hierarchy from the leaf nodes
> > (thus skipping the processor core level).
> >
> > Currently the ID provided is the offset of the Processor
> > Hierarchy Nodes Structure within PPTT. Whilst this is unique
> > it is not terribly elegant so alternative suggestions welcome.
> >
> > Note that arm64 / ACPI does not provide any means of identifying
> > a die level in the topology but that may be unrelate to the cluster
> > level.
> >
> > RFC questions:
> > 1) Naming
> > 2) Related to naming, do we want to represent all potential levels,
> > or this enough? On Kunpeng920, the next level up from cluster happens
> > to be covered by llc cache sharing, but in theory more than one
> > level of cluster description might be needed by some future system.
> > 3) Do we need DT code in place? I'm not sure any DT based ARM64
> > systems would have enough complexity for this to be useful.
> > 4) Other architectures? Is this useful on x86 for example?
> >
> > [1] ACPI Specification 6.3 - section 5.2.29.1 processor hierarchy node
> > structure (Type 0)
> > [2] https://github.com/hisilicon/hwloc/tree/linux-cluster
> >
> > Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> > ---
> >
> > Documentation/admin-guide/cputopology.rst | 26 ++++++++--
>
> You are adding new sysfs files here, but not adding Documentation/ABI/
> entries as well? This cputopology document is nice, but no one knows to
> look there for sysfs stuff :)
Hi Greg,
Ah. I'd assumed there wasn't a current doc as the patch adding
die description didn't touch it. Turns out it was just missing from
that patch. (Documentation/ABI/testing/sysfs-devices-system-cpu)
Seems those docs are missing quite a bit of more recent stuff such as
die and more package related parts. I'll bring it up to date as a
precursor to v2 of this series.
Thanks,
Jonathan
>
> thanks,
>
> greg k-h
next prev parent reply other threads:[~2020-10-19 8:10 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-16 15:27 [RFC PATCH] topology: Represent clusters of CPUs within a die Jonathan Cameron
2020-10-17 6:44 ` Greg Kroah-Hartman
2020-10-19 8:08 ` Jonathan Cameron [this message]
2020-10-19 10:00 ` Brice Goglin
2020-10-19 12:38 ` Jonathan Cameron
2020-10-19 10:01 ` Sudeep Holla
2020-10-19 13:14 ` Jonathan Cameron
2020-10-19 10:35 ` Peter Zijlstra
2020-10-19 12:32 ` Jonathan Cameron
2020-10-19 12:50 ` Peter Zijlstra
2020-10-19 13:12 ` Brice Goglin
2020-10-19 13:13 ` Morten Rasmussen
2020-10-19 13:10 ` Morten Rasmussen
2020-10-19 13:41 ` Jonathan Cameron
2020-10-19 14:16 ` Morten Rasmussen
2020-10-19 14:42 ` Brice Goglin
2020-10-19 15:30 ` Jonathan Cameron
2020-10-19 13:48 ` Valentin Schneider
2020-10-19 14:27 ` Jonathan Cameron
2020-10-19 15:51 ` Valentin Schneider
2020-10-19 16:00 ` Jonathan Cameron
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20201019080854.00001a9f@Huawei.com \
--to=jonathan.cameron@huawei.com \
--cc=Brice.Goglin@inria.fr \
--cc=gregkh@linuxfoundation.org \
--cc=guohanjun@huawei.com \
--cc=len.brown@intel.com \
--cc=linux-acpi@vger.kernel.org \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linuxarm@huawei.com \
--cc=sudeep.holla@arm.com \
--cc=will@kernel.org \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).