Hi,

I am bit confused by the sequence of events here and need some
clarification. Lets assume that CPU can go from 1 GHz to 1.5 GHz
without boost enabled and with boost it can go to 2 GHz.

On 17-01-25, 18:14, Lifeng Zheng wrote:

It turns out that cpuX will stay on the base frequency after performing
these operations:

1. boost all cpus: echo 1 > /sys/devices/system/cpu/cpufreq/boost

Boost enabled here, max_freq_req = 2 GHz.

2. offline the cpu: echo 0 > /sys/devices/system/cpu/cpuX/online

3. deboost all cpus: echo 0 > /sys/devices/system/cpu/cpufreq/boost

4. online the cpu: echo 1 > /sys/devices/system/cpu/cpuX/online

Boost is disabled currently here, but max_freq_req = 2 GHz, which is
incorrect and the current change you are proposing fixes it I think.
But it is not what you are claiming to fix.

5. boost all cpus again: echo 1 > /sys/devices/system/cpu/cpufreq/boost

Boost enabled again here, and max_freq_req = 2 GHz is the correct
value.

So the CPU doesn't stay at base frequency here, but 2 GHz only.

This is because max_freq_req of the policy is not updated during the online
process, and the value of max_freq_req before the last offline is retained.

which was 2 GHz in your example.

When the CPU is boosted again, freq_qos_update_request() will do nothing
because the old value is the same as the new one. This causes the CPU stay
on the base frequency. Update max_freq_req  in cpufreq_online() will solve
this problem.

-- 
viresh