Re: [Qemu-devel] TCG multithread plan.

[Lluís Vilanova]

Frederic Konrad writes:

> Hi everybody,
> Here is the plan we will follow:

> We will be focusing - from the outset - on the end goal of multi-threaded TCG 
> in full system emulation mode. On the way, we expect this will ‘fix’ user 
> mode.

> The plan is:

> * Create one cache per CPU as a first step. We can do more next and share a 
> cache.
> * Update tb_* to add a pointer to their cache.
> * Add atomic instruction support to the TGC (first on ARM).
> * Make tb_invalidate work between all cache.
> * Modify main-loop for multi-thread.
> * Memory access (eg: for device) are not thread safe that need to be fixed. 
> Initial plan simply globally mutex memory accesses - this may be optimised 
> later.
> * For now, irq handler for CPU seems ok but we need to check.

> We will discuss this during the call tomorrow.

Is there any plan to have the notion of "memory coherency domains"? (shortened
as MCD in the wiki)

Even though it's not that useful now, it could be used in the future to relax
the atomicity of operations when different devices operate on different MCDs and
TCG is not able to map that into an atomic host operation (aka, has to use
locks). A system with a CPU and a GPU would be a good example of that.


Thanks,
  Lluis

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