Re: [Xen-ia64-devel] [PATCH 0/10] [RFC] performance tuning TAKE 3

[Atsushi SAKAI <sakaia@xxxxxxxxxxxxxx>]

Hi, Tristan

 Is there any plan to add a counter for vcpu migration counting?
I want to see the correlation with these patch.

Thanks,
Atsushi SAKAI
 



>Le Mercredi 09 Ao〓 2006 13:27, Isaku Yamahata a 馗rit :
>> Hi all
>Hi
>
>some comments enclosed.
>
>> These patches are for performance tuning TAKE 3.
>> They are for comment, review and evaluation.
>>
>> PATCHES:
>> - performace counter
>>   NEW
>> - per vcpu vhpt
>> - tlb tracking
>> - deferred page freeing
>> - p2m exposure
>>   NEW
>>
>> CHANGES:
>> - various bug fixes.
>>   especially deferred page freeing patch bug.
>>   It spoiled performance much.
>>
>> - performance counter
>>   added performance counter.
>>   I added these for evaluation of the patches.
>>   But I think some of them are usefull for normal use.
>>   Is there any objection for commit?
>I think they can be safely commited.
>
>> - P2M table exposure
>>   I also included test module for p2m exposure module.
>>   It showed that p2m conversion with p2m exposure is faster than
>>   the hypercall conversion at about order 2.
>>   So I think p2m exposure patch is acceptable.
>>
>>
>> PATCH DETAIL:
>> - per vcpu vhpt
>>   It focuses on vcpu migration between physical cpus.
>>   With credit scheduler, vcpu is heavily migrated.
>>   This patch tries to reduce vTLB flush when vcpu is migrated.
>Although I have no objection for integrating this patch I have some doubts 
>about the gain.
>If vcpus are heavily migrated, this is a real loss due to caches.
>If vcpus are not heavily migrated the gain should be in the noise.
>(Of course it depends on the weight!)
>
>> - tlb tracking
>>   It forcuses on grant table mapping.
>>   When page is unmapped, full vTLB flush is necessary.
>>   By tracking tlb insert on grant mapped page, full vTLB flush
>>   can be avoided.
>>   Especially vbd does only DMA, so dom0 doesn't insert tlb entry
>>   on the grant mapped page. In such case any vTLB flush isn't needed.
>>
>> - deferred page freeing
>>   When the page in which tlb insert isn't tracked is unmapped/zapped from
>>   domain, full vTLB flush is necessary again.
>>   Balloon driver and grant table page transfer is the case.
>>   This patch focuses on it.
>>   It tries to batch freeing/zapping page from domain in order
>>   to reduce full vTLB flush.
>>
>> - p2m exposure
>>   DMA paravirtualization requires the conversion from pseudo physical
>> address to machine address. Currently it is done by hypercall.
>>   This patch tries to reduce the conversion overhead by read-only
>>   mapping the xen p2m table to domain.
>
>Thank you for the optimization job.
>
>Tristan.
>
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