Setting cpufreq on one cpu not reflected on others

Bug #968482 reported by Paul Larson on 2012-03-29
This bug affects 1 person
Affects Status Importance Assigned to Milestone
big.LITTLE Reference Switcher
Fix Released
Dave Martin

Bug Description

Builds are happening with ASYNC set to false, and changing to a different cluster seems to change completely to that cluster (based on the fast model cluster instruction counter), but the cpufreq interface only indicates the change in frequency for the cpu it was made on. This was on an ubuntu build,
# uname -a
Linux linaro-nano 3.2.0-21-linaro-lt-vexpressdt-rtsm #21~lt~ci~20120326163306+1332780867~4f70ff9clinaro1-Ubuntu SMP T armv7l armv7l armv7l GNU/Linux

To illustrate:
 echo userspace > /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
[ 1263.824647] arm-bl-cpufreq: Switching to cluster 0
(...same for cpu1,2,3)
cat /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_cur_freq
cat /sys/devices/system/cpu/cpu1/cpufreq/cpuinfo_cur_freq
... same for all cpus.

Here's where it gets a bit strange...
root@linaro-nano:~# echo 100000 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_setspeed
[ 1537.768842] arm-bl-cpufreq: Switching to cluster 1
root@linaro-nano:~# cat /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_cur_freq
[ 1539.621826] arm-bl-cpufreq: Switching to cluster 1
root@linaro-nano:~# cat /sys/devices/system/cpu/cpu1/cpufreq/cpuinfo_cur_freq
[ 1546.701841] arm-bl-cpufreq: Switching to cluster 0
root@linaro-nano:~# cat /sys/devices/system/cpu/cpu3/cpufreq/cpuinfo_cur_freq

So there could actually be two bugs here. It looks like it's not reflecting the change on all cores (Talked to davem about this earlier today, who thinks he has a patch for that), and then there's this effect of occasionally switching the cluster back when catting the cpuinfo_cur_freq for another cpu after switching.

Changed in linaro-big-little-reference:
assignee: nobody → Dave Martin (dave-martin-arm)
Paul Larson (pwlars) wrote :

Avik and I both tested a fix in Dave's linux-3-arm tree, arm/vexpressdt-rtsm+arm-virt-bl_cpufreq branch and can no longer reproduce this bug using that kernel.

Changed in linaro-big-little-reference:
importance: Undecided → Medium
status: New → Fix Released
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