7e90ffb716
Kernel timekeeping is designed to keep the change in cycles (since the last timer interrupt) below max_cycles, which prevents multiplication overflow when converting cycles to nanoseconds. However, if timer interrupts stop, the calculation will eventually overflow. Add protection against that. Select GENERIC_VDSO_OVERFLOW_PROTECT so that max_cycles is made available in the VDSO data page. Check against max_cycles, falling back to a slower higher precision calculation. Take advantage of the opportunity to move masking and negative motion check into the slow path. The result is a calculation that has similar performance as before. Newer machines showed performance benefit, whereas older Skylake-based hardware such as Intel Kaby Lake was seen <1% worse. Suggested-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Adrian Hunter <adrian.hunter@intel.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Link: https://lore.kernel.org/r/20240325064023.2997-9-adrian.hunter@intel.com |
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| .. | ||
| clocksource.h | ||
| gettimeofday.h | ||
| processor.h | ||
| vsyscall.h | ||