Dan Magenheimer wrote on Fri, 23 Apr 2010 at 07:09:57:
> While I like the direction this is going, please try to extend
> your model to cover the cases of ballooning and live-migration.
> For example, for "CONFINE", ballooning should probably be
> disallowed as pages surrendered on "this node" via ballooning
> may be only recoverable later on a different node. Similarly,
> creating a CONFINE guest is defined to fail if there is
> insufficient memory on any node... will live migration to a
> different physical machine similarly fail, even if an administrator
> explicitly requests it?
For the memory resources, I think we can use the same allocation strategies for
the live-migration cases. In general, the memory allocation strategy should be
_inherited_ upon live-migration. For example, if a NUMA guest is created with
SPLIT, it is guaranteed that the memory allocation strategy will be SPLIT at
live-migration time. If AUTOMATIC is used, the memory topology may change upon
live-migration. The guest will continue to run, but the NUMA memory topology in
the guest may not reflect the underlying hardware conditions. We may be able to
use some PV technique to re-initialize the memory subsystem in the guest when
updating the memory topology.
>
> In general, communicating NUMA topology to a guest is a "performance
> thing" and ballooning and live-migration are "flexibility things";
> and performance and flexibility mix like oil and water.
>
>> -----Original Message----- From: Andre Przywara
>> [mailto:andre.przywara@xxxxxxx] Sent: Friday, April 23, 2010 6:46 AM
>> To: Cui, Dexuan; Dulloor; xen-devel Cc: Nakajima, Jun Subject:
>> [Xen-devel] NUMA guest config options (was: Re: [PATCH 00/11] PV NUMA
>> Guests)
>>
>> Hi,
>>
>> yesterday Dulloor, Jun and I had a discussion about the NUMA guest
>> configuration scheme, we came to the following conclusions: 1. The
>> configuration would be the same for HVM and PV guests, only the
>> internal method of propagation would differ. 2. We want to make it as
>> easy as possible, with best performance out of the box as the design
>> goal. Another goal is predictable performance. 3. We (at least for now)
>> omit more sophisticated tuning options (exact user-driven description
>> of the guest's topology), so the guest's resources are split equally
>> across the guest nodes. 4. We have three basic strategies:
>> - CONFINE: let the guest use only one node. If that does not work,
>> fail. - SPLIT: allocate resources from multiple nodes, inject a NUMA
>> topology into the guest (includes PV querying via hypercall). If the
>> guest is paravirtualized and does not know about NUMA (missing ELF
>> hint): fail.
>> - STRIPE: allocate the memory in an interleaved way from multiple
>> nodes, don't tell the guest about NUMA at all.
>>
>> If any one the above strategies is explicitly specified in the config
>> file and it cannot be met, then the guest creation will fail.
>> A fourth option would be the default: AUTOMATIC. This will try the
>> three
>> strategies after each other (order: CONFINE, SPLIT, STRIP). If one
>> fails, the next will be tried (this will never use striping for HVM
>> guests).
>>
>> 5. The number of guest nodes is internally specified via a min/max
>> pair.
>> By default min is 1, max is the number of system nodes. The algorithm
>> will try to use the smallest possible number of nodes.
>>
>> The question remaining is whether we want to expose this pair to the
>> user:
>> - For predictable performance we want to specify an exact number of
>> guest nodes, so set min=max=<number of nodes> - For best performance,
>> the number of nodes should be at small as
>> possible, so min is always 1. For the explicit CONFINE strategy, max
>> would also be one, for AUTOMATIC it should be as few as possible, which
>> is already built in the algorithm. So it is not clear if "max nodes" is
>> a useful option. If it would serve as an upper boundary, then it is
>> questionable whether "failing-if-not-possible" is a useful result.
>>
>> So maybe we get along with just one (optional) value: guestnodes. This
>> will be useful in the SPLIT case, where it specifies the number of
>> nodes the guest sees (for predictable performance). CONFINE internally
>> overrides this value with "1". If one would impose a limit on the
>> number of nodes, one would choose "AUTOMATIC" and set guestnodes to
>> this number. If single-node allocations fail, it will use as few nodes
>> as possible, not exceeding the specified number.
>>
>> Please comment on this.
>>
>> Thanks and regards,
>> Andre.
>>
>> --
>> Andre Przywara
>> AMD-Operating System Research Center (OSRC), Dresden, Germany
>> Tel: +49 351 448-3567-12
>>
>>
>> _______________________________________________
>> Xen-devel mailing list
>> Xen-devel@xxxxxxxxxxxxxxxxxxx
>> http://lists.xensource.com/xen-devel
Jun
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