cpufreq_driver_fast_switch(9)

✨ cpufreq_driver_fast_switch ✨

okay bestie, buckle up — this is a page from the Kernel API Manual (section 9, kernel developer vibes only 💅) and it's literally about changing a CPU's clock speed without going to sleep. iconic behavior honestly.

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🎀 NAME 🎀

cpufreq_driver_fast_switch — carry out a fast CPU frequency switch. that's it, that's the whole job. speed. no napping. periodt. 🔥

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🌸 SYNOPSIS 🌸

unsigned int cpufreq_driver_fast_switch(struct cpufreq_policy *policy,
                                        unsigned int target_freq);

two args, one unsigned int back. short and sweet, the way we like it 🫶

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💖 ARGUMENTS 💖

• policy — the cpufreq policy you're switching the frequency for. like, which CPU crew we're doing this to 🧚
• target_freq — the new frequency you want to set. and ngl, it may be approximate — you're giving a vibe, not a promise ✨

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🦋 DESCRIPTION 🦋

carry out a fast frequency switch without sleeping. yes bestie, no sleeping on the job 😴🚫

the driver's ->fast_switch callback that this function invokes? it has to be suitable for being called from within RCU-sched read-side critical sections. so like, no funny business in there. it's also expected to select the minimum available frequency greater than or equal to target_freq — that's CPUFREQ_RELATION_L, iykyk 💅

🚨 important, bestie: this function must not be called if policy->fast_switch_enabled is unset. unset = hard no. do not pass go. do not collect $200 😭

governors that call this function have to guarantee two things, fr fr:

• it will never be invoked twice in parallel for the same policy
• it will never be called in parallel with either ->target or ->target_index for the same policy

basically: one at a time, no overlapping, we're not doing chaos today 🙈

returns the actual frequency set for the CPU. 🎯

and if the driver's ->fast_switch callback returns 0 to indicate an error condition — bestie, the hardware configuration must be preserved. don't touch anything, just back away slowly 💀

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👑 SEE ALSO 👑

kernel file ./drivers/cpufreq/cpufreq.c — and the whole extended family, all invited to the group chat 🫶:

• cpufreq_cpu_get(9)
• cpufreq_cpu_put(9)
• adjust_jiffies(9)
• cpufreq_notify_transition(9)
• cpufreq_enable_fast_switch(9)
• cpufreq_disable_fast_switch(9)
• cpufreq_driver_resolve_freq(9)
• cpufreq_parse_governor(9)
• cpufreq_add_dev(9)
• cpufreq_out_of_sync(9)
• cpufreq_quick_get(9)
• cpufreq_quick_get_max(9)
• cpufreq_get_hw_max_freq(9)
• cpufreq_get(9)
• cpufreq_suspend(9)
• cpufreq_resume(9)
• cpufreq_driver_test_flags(9)
• cpufreq_get_current_driver(9)
• cpufreq_get_driver_data(9)
• cpufreq_register_notifier(9)
• cpufreq_unregister_notifier(9)
• cpufreq_driver_adjust_perf(9)
• cpufreq_driver_has_adjust_perf(9)
• cpufreq_update_pressure(9)
• cpufreq_set_policy(9)
• cpufreq_update_policy(9)
• cpufreq_update_limits(9)
• cpufreq_register_driver(9)

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💫 and that's the page, bestie 💫

this little masterpiece lives in ./drivers/cpufreq, comes to you courtesy of the Kernel API Manual, and was dated October 2026 — go forth and switch frequencies fast, safely, and with main character energy 👑💜