diff options
| -rw-r--r-- | init/calibrate.c | 57 |
1 files changed, 34 insertions, 23 deletions
diff --git a/init/calibrate.c b/init/calibrate.c index b71643a7acae..f9000dfbe227 100644 --- a/init/calibrate.c +++ b/init/calibrate.c @@ -110,8 +110,8 @@ static unsigned long __cpuinit calibrate_delay_direct(void) {return 0;} /* * This is the number of bits of precision for the loops_per_jiffy. Each - * bit takes on average 1.5/HZ seconds. This (like the original) is a little - * better than 1% + * time we refine our estimate after the first takes 1.5/HZ seconds, so try + * to start with a good estimate. * For the boot cpu we can skip the delay calibration and assign it a value * calculated based on the timer frequency. * For the rest of the CPUs we cannot assume that the timer frequency is same as @@ -121,38 +121,49 @@ static unsigned long __cpuinit calibrate_delay_direct(void) {return 0;} static unsigned long __cpuinit calibrate_delay_converge(void) { - unsigned long lpj, ticks, loopbit; - int lps_precision = LPS_PREC; + /* First stage - slowly accelerate to find initial bounds */ + unsigned long lpj, ticks, loopadd, chop_limit; + int trials = 0, band = 0, trial_in_band = 0; lpj = (1<<12); - while ((lpj <<= 1) != 0) { - /* wait for "start of" clock tick */ - ticks = jiffies; - while (ticks == jiffies) - /* nothing */; - /* Go .. */ - ticks = jiffies; - __delay(lpj); - ticks = jiffies - ticks; - if (ticks) - break; - } + + /* wait for "start of" clock tick */ + ticks = jiffies; + while (ticks == jiffies) + ; /* nothing */ + /* Go .. */ + ticks = jiffies; + do { + if (++trial_in_band == (1<<band)) { + ++band; + trial_in_band = 0; + } + __delay(lpj * band); + trials += band; + } while (ticks == jiffies); + /* + * We overshot, so retreat to a clear underestimate. Then estimate + * the largest likely undershoot. This defines our chop bounds. + */ + trials -= band; + loopadd = lpj * band; + lpj *= trials; + chop_limit = lpj >> (LPS_PREC + 1); /* * Do a binary approximation to get lpj set to - * equal one clock (up to lps_precision bits) + * equal one clock (up to LPS_PREC bits) */ - lpj >>= 1; - loopbit = lpj; - while (lps_precision-- && (loopbit >>= 1)) { - lpj |= loopbit; + while (loopadd > chop_limit) { + lpj += loopadd; ticks = jiffies; while (ticks == jiffies) - /* nothing */; + ; /* nothing */ ticks = jiffies; __delay(lpj); if (jiffies != ticks) /* longer than 1 tick */ - lpj &= ~loopbit; + lpj -= loopadd; + loopadd >>= 1; } return lpj; |