X-Git-Url: http://ftp.safe.ca/?a=blobdiff_plain;f=init%2Fcalibrate.c;h=6eb48e53d61c58869bdc8aa5250397a2594ab0e3;hb=649233562cb1e83ebd2af30bd981881e51961b8b;hp=c698e04a3dbe37745b9b32cb696b1f5deb3f3acb;hpb=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2;p=safe%2Fjmp%2Flinux-2.6 diff --git a/init/calibrate.c b/init/calibrate.c index c698e04..6eb48e5 100644 --- a/init/calibrate.c +++ b/init/calibrate.c @@ -4,11 +4,14 @@ * Copyright (C) 1991, 1992 Linus Torvalds */ -#include +#include #include #include +#include +#include -static unsigned long preset_lpj; +unsigned long lpj_fine; +unsigned long preset_lpj; static int __init lpj_setup(char *str) { preset_lpj = simple_strtoul(str,NULL,0); @@ -17,28 +20,129 @@ 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 __cpuinit calibrate_delay_direct(void) +{ + unsigned long pre_start, start, post_start; + unsigned long pre_end, end, post_end; + unsigned long start_jiffies; + unsigned long timer_rate_min, timer_rate_max; + unsigned long good_timer_sum = 0; + unsigned long good_timer_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); + + timer_rate_max = (post_end - pre_start) / + DELAY_CALIBRATION_TICKS; + timer_rate_min = (pre_end - post_start) / + DELAY_CALIBRATION_TICKS; + + /* + * If the upper limit and lower limit of the timer_rate is + * >= 12.5% apart, redo calibration. + */ + if (pre_start != 0 && pre_end != 0 && + (timer_rate_max - timer_rate_min) < (timer_rate_max >> 3)) { + good_timer_count++; + good_timer_sum += timer_rate_max; + } + } + + if (good_timer_count) + return (good_timer_sum/good_timer_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 __cpuinit 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 * better than 1% + * 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 + * the cpu frequency, hence do the calibration for those. */ #define LPS_PREC 8 -void __devinit calibrate_delay(void) +void __cpuinit calibrate_delay(void) { unsigned long ticks, loopbit; int lps_precision = LPS_PREC; + static bool printed; if (preset_lpj) { loops_per_jiffy = preset_lpj; - printk("Calibrating delay loop (skipped)... " - "%lu.%02lu BogoMIPS preset\n", - loops_per_jiffy/(500000/HZ), - (loops_per_jiffy/(5000/HZ)) % 100); + if (!printed) + pr_info("Calibrating delay loop (skipped) " + "preset value.. "); + } else if ((!printed) && lpj_fine) { + loops_per_jiffy = lpj_fine; + pr_info("Calibrating delay loop (skipped), " + "value calculated using timer frequency.. "); + } else if ((loops_per_jiffy = calibrate_delay_direct()) != 0) { + if (!printed) + pr_info("Calibrating delay using timer " + "specific routine.. "); } else { loops_per_jiffy = (1<<12); - printk(KERN_DEBUG "Calibrating delay loop... "); + if (!printed) + pr_info("Calibrating delay loop... "); while ((loops_per_jiffy <<= 1) != 0) { /* wait for "start of" clock tick */ ticks = jiffies; @@ -68,12 +172,11 @@ void __devinit calibrate_delay(void) if (jiffies != ticks) /* longer than 1 tick */ loops_per_jiffy &= ~loopbit; } - - /* Round the value and print it */ - printk("%lu.%02lu BogoMIPS (lpj=%lu)\n", - loops_per_jiffy/(500000/HZ), - (loops_per_jiffy/(5000/HZ)) % 100, - loops_per_jiffy); } + if (!printed) + pr_cont("%lu.%02lu BogoMIPS (lpj=%lu)\n", + loops_per_jiffy/(500000/HZ), + (loops_per_jiffy/(5000/HZ)) % 100, loops_per_jiffy); + printed = true; }