Re: [v4][PATCH 11/19] tools: introduce some new parameters to set rdm policy

From: "Chen, Tiejun" <tiejun.chen@intel.com>
To: Ian Campbell <ian.campbell@citrix.com>
Cc: Wei Liu <wei.liu2@citrix.com>,
	Stefano Stabellini <stefano.stabellini@eu.citrix.com>,
	Ian Jackson <ian.jackson@eu.citrix.com>,
	xen-devel@lists.xen.org
Subject: Re: [v4][PATCH 11/19] tools: introduce some new parameters to set rdm policy
Date: Fri, 26 Jun 2015 17:36:19 +0800	[thread overview]
Message-ID: <558D1D13.2010208@intel.com> (raw)
In-Reply-To: <1435309027.32500.142.camel@citrix.com>

>> TODO: in the future this parameter may be further extended to allow
>> specifying arbitrary regions, e.g. even those belonging to another
>> platform as a preparation for live migration with passthrough devices.
>
> I don't think this needs to be explained in this document at all.
> Whenever someone does that work they can update the docs to describe the
> new functionality.

Okay.

>
>>
>> ...
>>
>>>
>>>> +
>>>> +"none" means we have nothing to do all reserved regions and ignore all policies,

[snip]

>> Just let me rephrase this,
>>
>> "none" means we don't check any reserved regions and then all rdm
>> policies would be ignored, so guest just work as before.
>
> When or why would I write:
>          rdm = "none"
> in my configuration file instead of just not saying anything?

As you know we just have two options, "none" vs. "host". So we need a 
explicit flag as a default libxl value to work out our mechanism.

+libxl_rdm_reserve_type = Enumeration("rdm_reserve_type", [
+    (0, "none"),
+    (1, "host"),
+    ])
+

We just think this name can make sense, right?

>
>
>>> Having read all these docs I now know what all the options are, but I
>>> still don't really know what I should write. I think an example or two
>>> of real world usage would be helpful.
>>
>> Here I picked some code fragments to help you understand this,
>
> I meant an example or two in the documentation.
>
> The code fragment didn't answer my question either, but that's not
> really the point.

Do you mean I should write two example, respectively?

#1. What is one actual conflict?
#2. After we're trying to fix this conflict,
#2.1 How will "strict" fail a VM?
#2.2 How will "relaxed" impact on a VM?

>
>>>
>>>> +Note this may be overridden by rdm_reserve option in PCI device configuration.
>>>> +

[snip]

>>> Rather than "above" (which is quite a large block of text) you should
>>> specifically mention the rdm option.
>>>
>>
>> What about this?
>>
>> (HVM/x86 only) This is same as reserve option inside the rdm option
>> but just specific to a given device, and "strict" is default here.
>
> Is strict the default everywhere or does it differ depending on the
> context?

The latter. We have two cases, a global case and a per device case, and 
they're different at this point.

Thanks
Tiejun