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

[Richard Henderson <rth@twiddle.net>]

On 10/01/2015 06:05 PM, alvise rigo wrote:
> On Wed, Sep 30, 2015 at 10:42 PM, Richard Henderson <rth@twiddle.net> wrote:
>>
>> On 09/30/2015 07:46 PM, alvise rigo wrote:
>>>
>>> On Wed, Sep 30, 2015 at 5:58 AM, Richard Henderson <rth@twiddle.net> 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.

Does it actually help, or is that a guess without numbers?


r~