On 23/08/17 08:23, Leo Yan wrote: > In the coresight CPU debug document it suggests to use 'echo' command > to set latency request to /dev/cpu_dma_latency so can disable all CPU > idle states, but in fact this doesn't work. > > This is because when the command 'echo' exits, it releases the device > node's file descriptor and the kernel release function removes the QoS > constraint; finally when the command 'echo' finished there have no > constraint imposed on cpu_dma_latency. > > This patch changes to use 'exec' to access '/dev/cpu_dma_latency', the > command 'exec' can avoid the file descriptor to be closed so we can > keep the constraint on cpu_dma_latency. > > This patch also corrects the description when set latency = 0uS, in > this case the idle state0 still can be selected by CPUIdle governor so > this means on ARM platform the 'WFI' state is still enabled, but all > other deeper states have been disabled so CPUs will not be powered off. > IMO, we should just refer to cpuidle and PM QoS documents from here so that any updates or changes in those documents are observed. Having a copy of the text may result in it getting obsolete. -- Regards, Sudeep -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
