clocks_calc_max_nsecs(9)

clocks_calc_max_nsecs(9) 💖

okay so bestie, this lil page is from the Kernel API Manual, and it’s all about clocks_calc_max_nsecs — the function whose whole vibe is “what’s the maximum nanoseconds we can convert before overflow ruins the party?” ✨

🌸 NAME 🌸

clocks_calc_max_nsecs — returns maximum nanoseconds that can be converted. That’s it, that’s the function, and honestly it ate. 💅

🦋 SYNOPSIS 🦋

u64 clocks_calc_max_nsecs (u32 mult , u32 shift , u32 maxadj , u64 mask
, u64 *max_cyc );

This is the exact call, no edits, no remix — the signature said what it said. 🫶

🎀 ARGUMENTS 🎀

• mult — cycle to nanosecond multiplier. yes bestie, it multiplies.
• shift — cycle to nanosecond divisor (power of two). It’s the divisor, and it’s a power of two, important.
• maxadj — maximum adjustment value to mult (~11%). That ~11% is doing numbers, so keep it.
• mask — bitmask for two's complement subtraction of non 64 bit counters. literally the mask for that exact job.
• max_cyc — maximum cycle value before potential overflow (does not include any safety margin). Note the parenthetical: this one does not include any safety margin.

💜 NOTE 💜

okay so here’s the safety-margin tea: this function includes a safety margin of 50%. In other words, we return half the number of nanoseconds the hardware counter can technically cover. This is done so that we can potentially detect problems caused by delayed timers or bad hardware, which might result in time intervals that are larger than what the math used can handle without overflows. It’s giving “we left room for drama, because overflow is not cute” 😭💅

🔥 SEE ALSO 🔥

The kernel file is ./kernel/time/clocksource.c — go peek, iykyk. And these besties are also in the group chat:

• clocks_calc_mult_shift(9)
• clocksource_mark_unstable(9)
• clocksource_suspend_select(9)
• clocksource_start_suspend_timing(9)
• clocksource_stop_suspend_timing(9)
• clocksource_suspend(9)
• clocksource_resume(9)
• clocksource_touch_watchdog(9)
• clocksource_max_adjustment(9)
• clocksource_update_max_deferment(9)
• clocksource_select(9)
• __clocksource_update_freq_scale(9)
• __clocksource_register_scale(9)
• clocksource_unregister(9)
• current_clocksource_show(9)
• current_clocksource_store(9)
• unbind_clocksource_store(9)
• available_clocksource_show(9)
• boot_override_clocksource(9)
• boot_override_clock(9)

okay that’s the tea ☕ source/version: ./kernel/time, date: October 2026, page: clocks_calc_max_nsecs(9) — mwah 💋