Messages in this thread | | | Date | Mon, 10 Oct 2011 17:25:57 +0100 | From | Alan Cox <> | Subject | Re: [Question] PM-QoS: PM_QOS_CPU_DMA_LATENCY == interrupt latency? |
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On Mon, 10 Oct 2011 22:31:34 +0800 Ming Lei <tom.leiming@gmail.com> wrote:
> Hi, > > Looks like it is a bit difficult to understand PM_QOS_CPU_DMA_LATENCY > from the words' meaning. > > After searching from google, I don't find some useful information about > the root cause for introducing PM_QOS_CPU_DMA_LATENCY. I understand > it is very similar to interrupt latency. Also from the comment for > omap_pm_set_max_mpu_wakeup_lat in file[1], the description is basically same > with interrupt latency. > > >From comments of pm_qos_add_request usages in drivers, it can be understood > as interrupt latency too, IMO. > > So, could we think that PM_QOS_CPU_DMA_LATENCY is interrupt latency?
No. Well it may be on some platforms but it isn't the same thing. On some devices a DMA transfer doesn't need the CPU involved but needs the CPU to respond within a set timescale (eg for coherency or bus arbitration). It is not the same thing as IRQ latency.
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