linux-kernel - Re: [PATCH v2 1/4] cpufreq: Fix re-boost issue after hotplugging a cpu

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Message-ID: <20250120092119.ik63qbwqk4kgnupv@vireshk-i7>
Date: Mon, 20 Jan 2025 14:51:19 +0530
From: Viresh Kumar <viresh.kumar@...aro.org>
To: "zhenglifeng (A)" <zhenglifeng1@...wei.com>
Cc: rafael@...nel.org, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org, linuxarm@...wei.com,
	jonathan.cameron@...wei.com, zhanjie9@...ilicon.com,
	lihuisong@...wei.com, fanghao11@...wei.com
Subject: Re: [PATCH v2 1/4] cpufreq: Fix re-boost issue after hotplugging a
 cpu

On 20-01-25, 17:10, zhenglifeng (A) wrote:
> On 2025/1/20 16:27, Viresh Kumar wrote:
> > On 17-01-25, 18:14, Lifeng Zheng wrote:
> >> 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.
> 
> Since boost is disabled, policy->max and policy->cpuinfo.max_freq will be
> 1.5GHz, this limits the actual frequency of the final.

Okay, I was thinking about the case (!new_policy &&
cpufreq_driver->online), where cpufreq_table_validate_and_sort() isn't
called and max_freq isn't updated eventually. But for the other case,
we will see max-freq as 1.5GHz.

> >> 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.
> 
> In freq_qos_update_request(), if req->pnode.prio == new_value, it will
> directly return 0 and not excecute freq_qos_apply(), in which will refresh
> frequency. So the frequency will stay on base.

-- 
viresh