thank you Raz and Sitsofe, I just found another info - direct from Intel engineering (reply in green): http://softwarecommunity.intel.com/isn/Community/en-US/forums/thread/980598.aspx And other useful stuff: http://cs.smu.ca/~jamuir/rdtscpm1.pdf http://softwarecommunity.intel.com/isn/Community/en-US/forums/thread/980590.aspx On Sun, Sep 21, 2008 at 1:59 AM, Raz <raziebe@xxxxxxxxx> wrote: > 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 >> >> > -- Regards, Peter Teoh -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
