Cc'ing Rafael and PM list. On 28-09-15, 14:33, nishtala wrote: > Hi, > > I am using the Ubuntu distribution on Intel(R) Core(TM) i7-2760QM CPU @ 2.40GHz > with Kernel version: 3.14.5. > > I deactivated the intel_pstate driver and activated the acpi-cpufreq driver > with userspace governor. > > The cpu has frequency scaling from 0.8GHz to 2.4GHz. > > /sys/devices/system/cpu/cpu0/cpufreq/scaling_set_speed I write to this file > using a shell script. > > Problem: When running 4 applications on 4 cores with 4 different frequency > sets, lets say 0.8GHz, 1.4GHz, 2.0GHz and 2.4GHz for cores 0, 1, 2 and 3. > Hyperthreading is turned off. All cores assume the frequency of the highest > core. I show this using the total clock time taken. > > Question:Is it actually possible for the 4 cores to be 4 different frequencies? if yes, how? > > These are the following set of experiments I performed to prove the > aforementioned hypothesis: > > 1. Run the application (say SPECcpu2006 benchmark 473.astar) in isolation on > core 0 with frequency 0.8GHz. The total time taken is 500seconds. > > Run the same application in isolation on core 0 with frequency 2.4GHz. The > total time taken is 194 seconds. > > The frequency of the other cores is irrelevant as long as they are idle. > > 2. Run the same application on core 0 with frequency 0.8GHz. And run a stress > benchmark (compute intensive, with no memory accesses) on core 1/2/3 at > 2.4GHz. Observe that the total time taken is also 194 seconds. Which does > not make sense, since the application is running on core 0 which is at > 0.8GHz and it should take ~500 seconds. > 3. Run the 4 instances of the application in parallel on 4 cores at 0.8GHz, > 1.4GHz, 2.0GHz and 2.4GHz. You'll observe that the application on the > smallest core: core 0:0.8GHz will finish at the same time as the > application on core3: 2.4GHz. Which in ideal world should not be the case. > > Do you have a possible explanation for this? I do not understand why this might > happen? or what I am missing out here? Can you give output of this please: grep . /sys/devices/system/cpu/cpu*/cpufreq/* -- viresh
