Re: [Qemu-devel] Update on TCG Multithreading

[Lluís Vilanova]

Alexander Graf writes:

> On 01.12.14 22:00, Lluís Vilanova wrote:
>> Mark Burton writes:
>> 
>>> All - first a huge thanks for those who have contributed, and those who have
>>> expressed an interest in helping out.
>> 
>>> One issue I’d like to see more opinions on is the question of a cache per 
>>> core,
>>> or a shared cache.
>>> I have heard anecdotal evidence that a shared cache gives a major 
>>> performance
>>> benefit….
>>> Does anybody have anything more concrete?
>>> (of course we will get numbers in the end if we implement the hybrid scheme 
>>> as
>>> suggested in the wiki - but I’d still appreciate any feedback).
>> 
>> I think it makes sense to have a per-core pointer to a qom TCGCacheClass. 
>> That
>> can then have its own methods for working with updates, making it much 
>> simpler
>> to work with different implementations, like completely avoiding locks 
>> (per-cpu
>> cache) or a hybrid approach like the one described in the wiki.

> I don't think you want to have indirect function calls in the fast path ;).

Ooops, true; at least probably, since you're never sure how much the HW
prefetcher is going to outsmart you :)

Well, I guess that a define will have to do then. But I think it still makes
sense to refactor tb_* functions and such to have a TCGCache as first argument.


Best,
  Lluis

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