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SubjectRe: [Question] PM-QoS: PM_QOS_CPU_DMA_LATENCY == interrupt latency?
From
2011/10/11 Ming Lei <tom.leiming@gmail.com>:
> Hi,
>
> On Tue, Oct 11, 2011 at 9:49 AM, Shaohua Li <shli@kernel.org> wrote:
>
>> As Alan explained, PM_QOS_CPU_DMA_LATENCY is for dma snooping. For example,
>> in x86, cpu snoop dma. when cpu is in idle state, cpu need snoop
>> device dma activity, there
>> is latency involved for idle state.
>>
>
> I see, thanks for your clarification.
>
> I also have two further questions about it:
>
> - Except for dma snooping purpose, are there any other cases in which
> PM_QOS_CPU_DMA_LATENCY is required?
it's the main motivation, IIRC, don't know other platforms

> - Are all CPUs required to be involved to dma snoop? Or only one CPU
> is enough? If one is enough, maybe we can allow other CPUs to reach
> deeper idle state.
then how can you make cache coherency between the cpus?


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