Re: [Xen-devel] [PATCH v2 3/7] x86: detect and initialize Intel CAT feature

[Dario Faggioli <dario.faggioli@xxxxxxxxxx>]

On Thu, 2015-03-19 at 18:41 +0800, Chao Peng wrote:

> diff --git a/docs/misc/xen-command-line.markdown 
> b/docs/misc/xen-command-line.markdown
> index 63871cb..768c55f 100644
> --- a/docs/misc/xen-command-line.markdown
> +++ b/docs/misc/xen-command-line.markdown
> @@ -1090,9 +1090,9 @@ This option can be specified more than once (up to 8 
> times at present).
>  > `= <integer>`
>  
>  ### psr (Intel)
> -> `= List of ( cmt:<boolean> | rmid_max:<integer> )`
> +> `= List of ( cmt:<boolean> | rmid_max:<integer> | cat:<boolean> | 
> num_sockets:<interger> )`
>
As Tim, I also don't like the 'num_sockets' part of the interface.

Actually, I'm not sure I understand what the idea behind this parameter
is. You say:
 
> +* Cache Alllocation Technology (Broadwell and later).  Information regarding
> +  the cache allocation.
> +  * `cat` instructs Xen to enable/disable Cache Allocation Technology.
> +  * `num_sockets` indicates the number of available sockets for CAT feature
> +    detection. All the sockets up to num_sockets will be checked for CAT
> +    feature. 
>
What it the use case of specifying, say, num_sockets=2, on a 4 socket
system? 

Is it for making it possible for the user to disable the feature on some
of the socket? If yes, I think it does make sense, but then why always
the last ones? shouldn't this be a list of socket  IDs?

Something like:

 sockets=0,2

meaning that the user wants the feature enabled _exactly_ on socket 0
and 2 (if available there, of course).

Regards,
Dario

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