From: Morten Rasmussen <morten.rasmussen@arm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Jonathan Cameron <Jonathan.Cameron@huawei.com>,
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>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Sudeep Holla <sudeep.holla@arm.com>,
guohanjun@huawei.com, Will Deacon <will@kernel.org>,
linuxarm@huawei.com, Brice Goglin <Brice.Goglin@inria.fr>,
valentin.schneider@arm.com
Subject: Re: [RFC PATCH] topology: Represent clusters of CPUs within a die.
Date: Mon, 19 Oct 2020 15:13:30 +0200 [thread overview]
Message-ID: <20201019131330.GD8004@e123083-lin> (raw)
In-Reply-To: <20201019125053.GM2628@hirez.programming.kicks-ass.net>
On Mon, Oct 19, 2020 at 02:50:53PM +0200, Peter Zijlstra wrote:
> On Mon, Oct 19, 2020 at 01:32:26PM +0100, Jonathan Cameron wrote:
> > On Mon, 19 Oct 2020 12:35:22 +0200
> > Peter Zijlstra <peterz@infradead.org> wrote:
>
> > > I'm confused by all of this. The core level is exactly what you seem to
> > > want.
> >
> > It's the level above the core, whether in an multi-threaded core
> > or a single threaded core. This may correspond to the level
> > at which caches are shared (typically L3). Cores are already well
> > represented via thread_siblings and similar. Extra confusion is that
> > the current core_siblings (deprecated) sysfs interface, actually reflects
> > the package level and ignores anything in between core and
> > package (such as die on x86)
>
> That seems wrong. core-mask should be whatever cores share L3. So on a
> Intel Core2-Quad (just to pick an example) you should have 4 CPU in a
> package, but only 2 CPUs for the core-mask.
>
> It just so happens that L3 and package were the same for a long while in
> x86 land, although recent chips started breaking that trend.
>
> And I know nothing about the core-mask being depricated; it's what the
> scheduler uses. It's not going anywhere.
Don't get confused over the user-space topology and the scheduler
topology, they are _not_ the same despite having similar names for some
things :-)
> So if your 'cluster' is a group of single cores (possibly with SMT) that
> do not share cache but have a faster cache connection and you want them
> to behave as-if they were a multi-core group that did share cache, then
> core-mask it is.
In the scheduler, yes. There is no core-mask exposed to user-space.
We have to be clear about whether we discuss scheduler or user-space
topology :-)
next prev parent reply other threads:[~2020-10-19 13:13 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
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 [this message]
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
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