Messages in this thread | | | Date | Tue, 11 Oct 2011 10:26:47 +0800 | Subject | Re: [Question] PM-QoS: PM_QOS_CPU_DMA_LATENCY == interrupt latency? | From | Shaohua Li <> |
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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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