Re: PML (Page Modification Logging) design for Xen

[Kai Huang <kai.huang@linux.intel.com>]

On 03/24/2015 03:53 PM, Jan Beulich wrote:
>>>> On 24.03.15 at 07:42, <kai.huang@linux.intel.com> wrote:
>> On 02/17/2015 06:19 PM, Jan Beulich wrote:
>>>>>> On 12.02.15 at 03:39, <kai.huang@linux.intel.com> wrote:
>>>> On 02/11/2015 07:52 PM, Andrew Cooper wrote:
>>>>> On 11/02/15 08:28, Kai Huang wrote:
>>>>>> Design
>>>>>> ======
>>>>>>
>>>>>> - PML feature is used globally
>>>>>>
>>>>>> A new Xen boot parameter, say 'opt_enable_pml', will be introduced to
>>>>>> control PML feature detection, and PML feature will only be detected
>>>>>> if opt_enable_pml = 1. Once PML feature is detected, it will be used
>>>>>> for dirty logging for all domains globally. Currently we don't support
>>>>>> to use PML on basis of per-domain as it will require additional
>>>>>> control from XL tool.
>>>>> Rather than adding in a new top level command line option for an ept
>>>>> subfeature, it would be preferable to add an "ept=" option which has
>>>>> "pml" as a sub boolean.
>>>> Which is good to me, if Jan agrees.
>>>>
>>>> Jan, which do you prefer here?
>>> A single "ept=" option as Andrew suggested.
>> Hi Andrew, Jan, Tim,
>>
>> Sorry to bring this thread back.
>>
>> Regarding to the parameter to control PML, I plan to enable PML by
>> default, in which case would a "ept=no-pml" be more reasonable to
>> disable it manually?
> Imo the default should be off at least initially.
OK.
>   The command line
> option parsing is (and should be) independent of the chosen
> default anyway, i.e. overrides in either direction should be
> possible.
While the parse_ept_param function does support "ept=pml" and 
"ept=no-pml" both, I think in the comments of the function we should 
explicitly tell whether to use "ept=pml" (in case PML is off by 
default), or "ept=no-pml" (in case PML is on by default), otherwise 
"ept=pml,no-pml" is legal but obviously it doesn't make any sense (and 
looks this issue also exists in parse_iommu_param?).

Thanks,
-Kai
>
>> Actually by referring to "iommu=" parameter, I would like to do below
>> changes. Is it good to you?
> Looks okay.
>
> Jan
>
>
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