On Fri, Mar 06, 2020 at 04:44:14PM +0100, Gerd Hoffmann wrote:
Factor out TimerKHz and ShiftTSC calculation to tsctimer_configure().
Signed-off-by: Gerd Hoffmann kraxel@redhat.com
src/hw/timer.c | 21 +++++++++++++-------- 1 file changed, 13 insertions(+), 8 deletions(-)
diff --git a/src/hw/timer.c b/src/hw/timer.c index bdcb3bfca211..ce3d63cd75f6 100644 --- a/src/hw/timer.c +++ b/src/hw/timer.c @@ -58,6 +58,18 @@ u8 ShiftTSC VARFSEG;
- Internal timer setup
****************************************************************/
+static void +tsctimer_configure(u64 t) +{
- while (t >= (1<<24)) {
ShiftTSC++;t = (t + 1) >> 1;- }
- TimerKHz = DIV_ROUND_UP((u32)t, 1000 * PMTIMER_TO_PIT);
- TimerPort = 0;
- dprintf(1, "CPU Mhz=%u\n", (TimerKHz << ShiftTSC) / 1000);
+}
#define CALIBRATE_COUNT 0x800 // Approx 1.7ms
// Calibrate the CPU time-stamp-counter @@ -87,14 +99,7 @@ tsctimer_setup(void) dprintf(6, "tsc calibrate start=%u end=%u diff=%u\n" , (u32)start, (u32)end, (u32)diff); u64 t = DIV_ROUND_UP(diff * PMTIMER_HZ, CALIBRATE_COUNT);
- while (t >= (1<<24)) {
ShiftTSC++;t = (t + 1) >> 1;- }
- TimerKHz = DIV_ROUND_UP((u32)t, 1000 * PMTIMER_TO_PIT);
- TimerPort = 0;
- dprintf(1, "CPU Mhz=%u\n", (TimerKHz << ShiftTSC) / 1000);
- tsctimer_configure(t);
}
The PMTIMER_TO_PIT in DIV_ROUND_UP((u32)t, 1000 * PMTIMER_TO_PIT) is directly tied to the measurement interval performed in tsctimer_setup(). Specifically, the code calculates the number of tsc ticks in n PIT intervals and then calculates "tsc_hz=pit_hz*elapsed_tsc/n". The complicated math is to avoid 64bit divides. I recommend against moving that low-level math to another function, as I fear the relationship would then be harder to understand.
-Kevin