On Mon, Oct 31, 2011 at 09:10:40PM +0000, David Laight wrote: > The problem is that getting an accurate timestamp is relatively > expensive. It has been almost the dominant part of process switch.
Let's make this a bit less vague for X86. The numbers are from memory, but should reflect the order of magnitude. Using TSC or LAPIC for gettimeofday requires in the order of 100-120 cycles, including system call overhead. Timer code is roughly half of that. Any other timer, including HPET and ACPI-fast are above the 1000 cycle barrier and completely inacceptable. Joerg
