linux-kernel - Re: [PATCHv4 08/13] Documentation/ABI: Add node performance attributes

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Date:   Thu, 17 Jan 2019 16:09:32 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Keith Busch <keith.busch@...el.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rafael Wysocki <rafael@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Dan Williams <dan.j.williams@...el.com>
Subject: Re: [PATCHv4 08/13] Documentation/ABI: Add node performance attributes

On Wed, Jan 16, 2019 at 6:59 PM Keith Busch <keith.busch@...el.com> wrote:
>
> Add descriptions for memory class initiator performance access attributes.

Again, I would combine this with the previous patch.

> Signed-off-by: Keith Busch <keith.busch@...el.com>
> ---
>  Documentation/ABI/stable/sysfs-devices-node | 28 ++++++++++++++++++++++++++++
>  1 file changed, 28 insertions(+)
>
> diff --git a/Documentation/ABI/stable/sysfs-devices-node b/Documentation/ABI/stable/sysfs-devices-node
> index a9c47b4b0eee..2217557f29d3 100644
> --- a/Documentation/ABI/stable/sysfs-devices-node
> +++ b/Documentation/ABI/stable/sysfs-devices-node
> @@ -114,3 +114,31 @@ 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.
> +
> +What:          /sys/devices/system/node/nodeX/classY/read_bandwidth
> +Date:          December 2018
> +Contact:       Keith Busch <keith.busch@...el.com>
> +Description:
> +               This node's read bandwidth in MB/s available to memory
> +               initiators in nodes found in this class's initiators_nodelist.
> +
> +What:          /sys/devices/system/node/nodeX/classY/read_latency
> +Date:          December 2018
> +Contact:       Keith Busch <keith.busch@...el.com>
> +Description:
> +               This node's read latency in nanoseconds available to memory
> +               initiators in nodes found in this class's initiators_nodelist.

I'm not sure if the term "read latency" is sufficient here.  Is this
the latency between sending a request and getting a response or
between sending the request and when the data actually becomes
available?

Moreover, is it the worst-case latency or the average latency?

> +
> +What:          /sys/devices/system/node/nodeX/classY/write_bandwidth
> +Date:          December 2018
> +Contact:       Keith Busch <keith.busch@...el.com>
> +Description:
> +               This node's write bandwidth in MB/s available to memory
> +               initiators in nodes found in this class's initiators_nodelist.
> +
> +What:          /sys/devices/system/node/nodeX/classY/write_latency
> +Date:          December 2018
> +Contact:       Keith Busch <keith.busch@...el.com>
> +Description:
> +               This node's write latency in nanoseconds available to memory
> +               initiators in nodes found in this class's initiators_nodelist.
> --

Same questions as for the read latency apply here.