From mboxrd@z Thu Jan 1 00:00:00 1970 From: kim.phillips@arm.com (Kim Phillips) Date: Thu, 15 Jun 2017 09:22:46 -0500 Subject: [PATCH 00/17] coresight: next v4.12-rc4 In-Reply-To: References: <1496693718-9191-1-git-send-email-mathieu.poirier@linaro.org> <20170609175339.28d1d4d5a6c91a9e16c16bf7@arm.com> <20170613161712.f1f3cac734939d8728c7ed77@arm.com> <20170614062229.GA28496@leoy-ThinkPad-T440> <20170614223453.3357117a7f25ee68924a071c@arm.com> Message-ID: <20170615092246.bc4fb71637e482a118199864@arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Thu, 15 Jun 2017 09:41:22 +0100 Sudeep Holla wrote: > On 15/06/17 04:34, Kim Phillips wrote: > [...] > > How does one tell whether writes to /dev/cpu_dma_latency are effective? > > > Watch /sys/devices/system/cpu/cpu*/cpuidle/state*/{usage,time}, they > shouldn't tick based on the value set to cpu_dma_latency. > > E.g. a value of 0 should stop entering all the idle states. I see all states following the same pattern whether 0 or not: root at juno:~# cat show2.sh show() { echo $1 > /dev/cpu_dma_latency echo === $1: cat /sys/devices/system/cpu/cpu2/cpuidle/state*/{usage,time} echo --- sleep 10 cat /sys/devices/system/cpu/cpu2/cpuidle/state*/{usage,time} } show 0 show 1500 show 0 root at juno:~# taskset -c 2 bash ./show2.sh === 0: 1893 894 5417 1398675 65997648 3818880750 --- 1895 905 5434 1401721 68076867 3826795502 === 1500: 1895 905 5434 1401721 68076867 3826795502 --- 1895 918 5447 1401721 69403510 3835466081 === 0: 1895 918 5447 1401721 69403510 3835466081 --- 1896 929 5463 1403577 71454839 3843409979 googling suggests the /dev/cpu_dma_latency file should be *kept* open, and written a 32-bit binary number: https://access.redhat.com/articles/65410 If so (I don't have time to test), this cpu debug documentation is very deceptive. Kim