Re: [PATCHv5 10/10] doc/mm: New documentation for memory performance

Keith Busch
2019-02-06T16:25:53Z

On Wed, Feb 06, 2019 at 10:45:52AM +0000, Jonathan Cameron wrote:
> On Thu, 24 Jan 2019 16:07:24 -0700
> Keith Busch <keith.busch@intel.com> wrote:
> > + # tree -P "read*|write*" /sys/devices/system/node/nodeY/access0/
> > + /sys/devices/system/node/nodeY/access0/
> > + |-- read_bandwidth
> > + |-- read_latency
> > + |-- write_bandwidth
> > + `-- write_latency
>
> These seem to be under
> /sys/devices/system/node/nodeY/access0/initiators/
> (so one directory deeper).

You're right, I used data from the previous series to generate that.

> > + # tree sys/devices/system/node/node0/side_cache/
> > + /sys/devices/system/node/node0/side_cache/
> > + |-- index1
> > + | |-- associativity
> > + | |-- level
>
> What is the purpose of having level in here? Isn't it the same as the A..C
> in the index naming?

Yes, it is redundant with the name. I will remove it.

> > + | |-- line_size
> > + | |-- size
> > + | `-- write_policy
> > +
> > +The "associativity" will be 0 if it is a direct-mapped cache, and non-zero
> > +for any other indexed based, multi-way associativity.
>
> Is it worth providing the ACPI mapping in this doc? We have None, Direct and
> 'complex'. Fun question of what None means? Not specified?

Yeah, my take on "none" was that it's unreported and we don't know what
is actually happening..

> > +
> > +The "level" is the distance from the far memory, and matches the number
> > +appended to its "index" directory.
> > +
> > +The "line_size" is the number of bytes accessed on a cache miss.
>
> Maybe "number of bytes accessed from next cache level" ?

Sounds good.