Re: [Qemu-devel] [RFC v5 3/6] softmmu: Add helpers for a new slowpath

[alvise rigo]

On Wed, Sep 30, 2015 at 10:42 PM, Richard Henderson <address@hidden> wrote:
>
> On 09/30/2015 07:46 PM, alvise rigo wrote:
>>
>> On Wed, Sep 30, 2015 at 5:58 AM, Richard Henderson <address@hidden> wrote:
>>>
>>> Why would you need to indicate that another cpu has started an exclusive
>>> operation on this page?  That seems definitely wrong.
>>
>>
>> The cpu_physical_memory_clear_excl_dirty() sets the flag to generate
>> the TLB entry with the EXCL flag.
>
>
> Yes, but surely the clearing of dirty on current_cpu is enough to cause the 
> other cpus to see that they need to set TLB_EXCL when reloading their tlb 
> entries.
>
> Why do you need to manipulate the *other* cpu's dirty bit?

Because then we can assume that a cpu with the bit cleared has for
sure the TLB entries with the EXCL flag set for that specific page.
Moreover, knowing which cpus have the EXCL flag set allows to reduce
the flushing requests whenever a new LL is issued on the same page.

>
>
>>> I wonder what can be done to clean all of this up, short of actually
>>> transitioning to c++ templates...
>>>
>>
>> Is there already an example in QEMU I can look at?
>
>
> No.

Thank,
alvise

>
>
>
> r~