The bellow is a list of Linux timers listed in Bovet's[1] Book. 2.1 PIT - programmable interval timer PIT is Linux default scheduler timer. Its frequency is 1KHZ at best. 2.2 TSC - Time Stamp counter All x86 processors include a CLK processor input pin. The processor has a timer which increases at each clock signal. This clock timer is read by "rdtscl" assembly command. With 2GHZ the time stamp counter will increment every 500 picoseconds. 2.3 RTC - Real time clock Real time clock (RTC) frequency is up to 8 KHz and accuracy is quite good. RTC is running on battery and is independent from the PC power. 2.4 HPET - High Precision Event timer High Precision Event timer is a new timer developed by Intel and Microsoft. It is a chip containing several 64bit or 32bit timer. Each timer frequency is at least 10Mhz. It raises a hardware interrupt every 100ns. 2.5 CPU Local Timer The Local APIC is in present x86 microprocessors. It is based on the bus clock signal. 2.6 PM - ACPI power management ACPI (Advanced configuration power interface) is resident in almost all ACPI-based motherboards. This is a simple counter with frequency 3.58 MHz. It does not generate any interrupts but accesses able through an I/O port. On Sat, Sep 20, 2008 at 1:28 PM, Sitsofe Wheeler <sitsofe@xxxxxxxxx> wrote: > Peter Teoh wrote: >> >> Q1: the assembly instruction: "rdtsc" will always get its clocking >> from PIT right? > > I doubt it. I believe on x86 RDTSC just reads a bunch of registers updated > by the CPU when it ticks. It's not really a separate programmable piece of > hardware. > >> Q2: the remark for select_clocksource() said it will select the >> best, but the function is a loopless, deterministic function that just >> return value from a linked list. Hm.....cannot understand it >> usage... > > You might want to trace execution from clocksource_register (and the > functions that end up being called from it) in that case to see HOW the list > is built. > > -- > To unsubscribe from this list: send an email with > "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx > Please read the FAQ at http://kernelnewbies.org/FAQ > > -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
