From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andrew Cooper <andrew.cooper3@citrix.com>
Subject: Re: [PATCH v2 2/8] x86: handle CQM resource when
 creating/destroying guests
Date: Mon, 25 Nov 2013 16:02:07 +0000
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To: "Xu, Dongxiao" <dongxiao.xu@intel.com>
Cc: Tim Deegan <tim@xen.org>, Keir Fraser <keir@xen.org>, Jan Beulich <JBeulich@suse.com>, "xen-devel@lists.xen.org" <xen-devel@lists.xen.org>
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On 25/11/13 03:21, Xu, Dongxiao wrote:
>
>>> +
>>> +    spin_lock_irqsave(&cqm_lock, flags);
>>> +    /* We do not free system reserved "RMID=0" */
>>> +    if ( rmid > 0 )
>>> +    {
>>> +        cqm_res_array[rmid].inuse = 0;
>>> +        cqm_res_array[rmid].domain_id = 0;
>> Would DOMID_INVALID be more appropriate here? 0 is valid domain
>> identifier.  It would also mean that you could remove the inuse flag
>> from the structure, and the structure itself degrades to an array of
>> domid_t's
>>
>> You can then further use cmpxchg() and avoid the spinlock.
>>
>> I guess this all depends on whether you are expecting to add new
>> information into the structure or not.
> Per my understanding, DOMID_xxx is somewhat related with memory management, e.g., DOMID_INVALID is used to identify pages with unknown owner. Is it appropriate to use it in CQM feature?
>
> According to your proposal:
>  - DOMID_INVALID is for RMIDs that are not allocated yet;
>  - A valid domain number stands for the RMID is used for a certain domain;
>  - Maybe DOMID_SELF or DOMID_XEN for the system reserved RMID=0?
>
> Do you think it is OK if we introduce extra meanings (CQM specific) for those macros?

CC'ing the relevant maintainers for their opinion.

I would suggest that DOMID_INVALID should have its formal meaning
expanded to any case where there can logically be a domid needing a
specific invalid state.

~Andrew