linux-kernel - Re: [PATCHv4 05/13] Documentation/ABI: Add new node sysfs attributes

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Date:   Fri, 18 Jan 2019 08:35:50 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     Jonathan Cameron <jonathan.cameron@...wei.com>
Cc:     Keith Busch <keith.busch@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux ACPI <linux-acpi@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rafael Wysocki <rafael@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>
Subject: Re: [PATCHv4 05/13] Documentation/ABI: Add new node sysfs attributes

On Fri, Jan 18, 2019 at 3:22 AM Jonathan Cameron
<jonathan.cameron@...wei.com> wrote:
>
> On Wed, 16 Jan 2019 10:57:56 -0700
> Keith Busch <keith.busch@...el.com> wrote:
>
> > Add entries for memory initiator and target node class attributes.
> >
> > Signed-off-by: Keith Busch <keith.busch@...el.com>
> > ---
> >  Documentation/ABI/stable/sysfs-devices-node | 25 ++++++++++++++++++++++++-
> >  1 file changed, 24 insertions(+), 1 deletion(-)
> >
> > diff --git a/Documentation/ABI/stable/sysfs-devices-node b/Documentation/ABI/stable/sysfs-devices-node
> > index 3e90e1f3bf0a..a9c47b4b0eee 100644
> > --- a/Documentation/ABI/stable/sysfs-devices-node
> > +++ b/Documentation/ABI/stable/sysfs-devices-node
> > @@ -90,4 +90,27 @@ Date:              December 2009
> >  Contact:     Lee Schermerhorn <lee.schermerhorn@...com>
> >  Description:
> >               The node's huge page size control/query attributes.
> > -             See Documentation/admin-guide/mm/hugetlbpage.rst
> > \ No newline at end of file
> > +             See Documentation/admin-guide/mm/hugetlbpage.rst
> > +
> > +What:                /sys/devices/system/node/nodeX/classY/
> > +Date:                December 2018
> > +Contact:     Keith Busch <keith.busch@...el.com>
> > +Description:
> > +             The node's relationship to other nodes for access class "Y".
> > +
> > +What:                /sys/devices/system/node/nodeX/classY/initiator_nodelist
> > +Date:                December 2018
> > +Contact:     Keith Busch <keith.busch@...el.com>
> > +Description:
> > +             The node list of memory initiators that have class "Y" access
> > +             to this node's memory. CPUs and other memory initiators in
> > +             nodes not in the list accessing this node's memory may have
> > +             different performance.
> > +
> > +What:                /sys/devices/system/node/nodeX/classY/target_nodelist
> > +Date:                December 2018
> > +Contact:     Keith Busch <keith.busch@...el.com>
> > +Description:
> > +             The node list of memory targets that this initiator node has
> > +             class "Y" access. Memory accesses from this node to nodes not
> > +             in this list may have differet performance.
>
> Different performance from what?  In the other thread we established that
> these target_nodelists are kind of a backwards reference, they all have
> their characteristics anyway.  Perhaps this just needs to say:
> "Memory access from this node to these targets may have different performance"?
>
> i.e. Don't make the assumption I did that they should all be the same!

I think a clarification of "class" is needed in this context. A
"class" is the the set of initiators that have the same rated
performance to a given target set. In other words "class" is a tuple
of (performance profile, initiator set, target set). Different
performance creates a different tuple / class.