Re: [Qemu-devel] [Qemu-ppc] [PATCH 2/2] tcg/ppc*: Move cache initialization to ppc specific code

[Alexander Graf <agraf@suse.de>]

On 04.10.2011, at 00:07, Scott Wood wrote:

> On 10/03/2011 05:06 PM, Alexander Graf wrote:
>> 
>> On 03.10.2011, at 23:50, Scott Wood wrote:
>> 
>>> On 10/03/2011 04:36 PM, Alexander Graf wrote:
>>>> With TCG, we're never executing guest code directly, but always go
>>>> through TCG to emulate it. So the only case where we actually need to
>>>> flush the icache is in TCG code generation, never outside, right?
>>> 
>>> Right.
>>> 
>>>> For KVM, I agree. We need some indication to flush the cache. But it
>>>> doesn't have to be done that complicated. We can simply do an inline
>>>> function that gets always called and has a few conditionals on when
>>>> to actually flush. That inline function could easily be a nop on
>>>> !ppc, though I'm not 100% sure that no other arch needs this.
>>> 
>>> It's already an inline function that's a nop on !ppc.  What
>>> simplification do you suggest?
>> 
>> Is flush_icache_range() always defined on all hosts with all compiler
>> variants that QEMU supports? If not, we should have a small wrapper
>> that explicitly makes it a nop on !ppc. CC'ing Paolo and Richard for
>> clarification.
> 
> It's defined in cache-utils.h using GCC-style inline asm, and is a no-op
> if _ARCH_PPC is not defined.

Ah, there it's hiding. It sounded a lot like the gcc built-in version.

So all we need is a nop'ing version in the !_ARCH_PPC case, right? And then later some way to make book3s fast again for coherent caching machines.


Alex