diff options
Diffstat (limited to 'init/calibrate.c')
| -rw-r--r-- | init/calibrate.c | 94 |
1 files changed, 94 insertions, 0 deletions
diff --git a/init/calibrate.c b/init/calibrate.c index c698e04a3dbe..d206c7548fe6 100644 --- a/init/calibrate.c +++ b/init/calibrate.c @@ -8,6 +8,8 @@ #include <linux/delay.h> #include <linux/init.h> +#include <asm/timex.h> + static unsigned long preset_lpj; static int __init lpj_setup(char *str) { @@ -17,6 +19,92 @@ static int __init lpj_setup(char *str) __setup("lpj=", lpj_setup); +#ifdef ARCH_HAS_READ_CURRENT_TIMER + +/* This routine uses the read_current_timer() routine and gets the + * loops per jiffy directly, instead of guessing it using delay(). + * Also, this code tries to handle non-maskable asynchronous events + * (like SMIs) + */ +#define DELAY_CALIBRATION_TICKS ((HZ < 100) ? 1 : (HZ/100)) +#define MAX_DIRECT_CALIBRATION_RETRIES 5 + +static unsigned long __devinit calibrate_delay_direct(void) +{ + unsigned long pre_start, start, post_start; + unsigned long pre_end, end, post_end; + unsigned long start_jiffies; + unsigned long tsc_rate_min, tsc_rate_max; + unsigned long good_tsc_sum = 0; + unsigned long good_tsc_count = 0; + int i; + + if (read_current_timer(&pre_start) < 0 ) + return 0; + + /* + * A simple loop like + * while ( jiffies < start_jiffies+1) + * start = read_current_timer(); + * will not do. As we don't really know whether jiffy switch + * happened first or timer_value was read first. And some asynchronous + * event can happen between these two events introducing errors in lpj. + * + * So, we do + * 1. pre_start <- When we are sure that jiffy switch hasn't happened + * 2. check jiffy switch + * 3. start <- timer value before or after jiffy switch + * 4. post_start <- When we are sure that jiffy switch has happened + * + * Note, we don't know anything about order of 2 and 3. + * Now, by looking at post_start and pre_start difference, we can + * check whether any asynchronous event happened or not + */ + + for (i = 0; i < MAX_DIRECT_CALIBRATION_RETRIES; i++) { + pre_start = 0; + read_current_timer(&start); + start_jiffies = jiffies; + while (jiffies <= (start_jiffies + 1)) { + pre_start = start; + read_current_timer(&start); + } + read_current_timer(&post_start); + + pre_end = 0; + end = post_start; + while (jiffies <= + (start_jiffies + 1 + DELAY_CALIBRATION_TICKS)) { + pre_end = end; + read_current_timer(&end); + } + read_current_timer(&post_end); + + tsc_rate_max = (post_end - pre_start) / DELAY_CALIBRATION_TICKS; + tsc_rate_min = (pre_end - post_start) / DELAY_CALIBRATION_TICKS; + + /* + * If the upper limit and lower limit of the tsc_rate is + * >= 12.5% apart, redo calibration. + */ + if (pre_start != 0 && pre_end != 0 && + (tsc_rate_max - tsc_rate_min) < (tsc_rate_max >> 3)) { + good_tsc_count++; + good_tsc_sum += tsc_rate_max; + } + } + + if (good_tsc_count) + return (good_tsc_sum/good_tsc_count); + + printk(KERN_WARNING "calibrate_delay_direct() failed to get a good " + "estimate for loops_per_jiffy.\nProbably due to long platform interrupts. Consider using \"lpj=\" boot option.\n"); + return 0; +} +#else +static unsigned long __devinit calibrate_delay_direct(void) {return 0;} +#endif + /* * 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 @@ -35,6 +123,12 @@ void __devinit calibrate_delay(void) "%lu.%02lu BogoMIPS preset\n", loops_per_jiffy/(500000/HZ), (loops_per_jiffy/(5000/HZ)) % 100); + } else if ((loops_per_jiffy = calibrate_delay_direct()) != 0) { + printk("Calibrating delay using timer specific routine.. "); + printk("%lu.%02lu BogoMIPS (lpj=%lu)\n", + loops_per_jiffy/(500000/HZ), + (loops_per_jiffy/(5000/HZ)) % 100, + loops_per_jiffy); } else { loops_per_jiffy = (1<<12); |