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xen-ia64-devel
RE: single software TLB vs. multiple software TLBs (was RE: [Xen-ia64-de
Tristan Gingold wrote:
> Le Mercredi 12 Avril 2006 10:57, Dong, Eddie a écrit :
>> Tristan:
>> You are probably avocating for the flexibility of hash TLB too from
>> the issue :-) Yes, when multiple TLBs are supported, i.e. hash TLB
>> here, those big guest page translations can be put into software TLB
>> using gmfn (leave to future tuning). When it is inserted into
>> machine TLB or VHPT, it can be breakdown to many small page size
>> translations (up to the balance of performance and functionality).
> No, you have to split and insert all entries!
>
Just make sure I am understanding correctly. With the help of software TLB for
guest huge translation, you have the flexibility to either breakdown it into
smaller ones to VHPT for all entries at a time, or you can do one at a time.
Defenitely several at a time is also OK if people want to :-)
That is another reason why we need multiple software TLBs. So far the
implementation of hash TLB addresses this issue preliminary. We must merge both
VTI and non VTI approach to reduce future maintaince effort (I guess you'd like
to see SMP works for both para and non-para domains too). Multiple software
tlbs are a must hereby.
So far the algorithm used for hash TLB and VHPT are very similar :-)
>> I.e. the machine rr4.ps could be 16KB for
>> guest vrr4.ps=256M. Another point is that VHPT hash uses VPN and rid
>> as hash index, here the VPN means 256M/16K=16K contiguous index. In
>> this way the hash result will be not duplicated as if the hash table
>> can accomodate 16K+ entries. So forward progress can be guaranteed
>> by the software TLB + VHPT.
>>
>> Hope this helpful!
> Ok it makes sense. If the VHPT is correctly sized it should work.
> [Maybe comments should be added somewhere to avoid future problem].
>
> Thanks
> Tristan.
Thx, Eddie
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