[maemo-developers] Where are the N900 "too much time at 600Mhz" safeguards?
From: Matan Ziv-Av matan at svgalib.orgDate: Thu Jan 28 01:25:44 EET 2010
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On Wed, 27 Jan 2010, Javier S. Pedro wrote: > When I got my N900, one of the first things I noticed is that (as measured by > powertop) I could never get a 100% ratio at 600 Mhz, but more like 95%. I > quickly assumed this was the safeguard for the issue Igor Stoppa talked about > at the Maemo Summit. > > However, I've noticed today (as suggested by a tmo post) that the above is not > caused by any special modification in the kernel, but rather because of the > CPU idling while waiting for the SGX / some other hw (so, testing methodology > failure on my part :) ). > > Thus, given any task bounded by raw CPU throughput, the device will happily > clock itself at 600Mhz, even for hours. Doesn't that contradict what Igor said > at the summit? At least for 30 minutes, there appear to be no 'safeguards': N900:~# date ; cat /sys/devices/system/cpu/cpu0/cpufreq/stats/time_in_state ; for i in ` seq 1 1000` ; do bzip2 -c9 /lib/libc-2.5.so > /dev/null ; done ; cat /sys/devices/system/cpu/cpu0/cpufreq/stats/time_in_state ; date Wed Jan 27 15:35:32 IST 2010 600000 43683 550000 487 500000 17132 250000 1164197 600000 254442 550000 487 500000 17132 250000 1164200 Wed Jan 27 16:10:39 IST 2010 This represents more than 99.99% of 35 minutes at 600MHz. Note that I ran this test with no SIM, screen off, not charging and wifi connected, but with practically no traffic. The device got only slightly warm, but it was hardly noticeable, so I guess that the power draw of the CPU, even at 600MHz does not have a large effect the system. BTW, is there a temperature sensor somewhere in the system like there is in the N810? -- Matan Ziv-Av. matan at svgalib.org
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