cregit-Linux how code gets into the kernel

Release 4.7 init/calibrate.c

Directory: init
/* calibrate.c: default delay calibration
 *
 * Excised from init/main.c
 *  Copyright (C) 1991, 1992  Linus Torvalds
 */

#include <linux/jiffies.h>
#include <linux/delay.h>
#include <linux/init.h>
#include <linux/timex.h>
#include <linux/smp.h>
#include <linux/percpu.h>


unsigned long lpj_fine;

unsigned long preset_lpj;

static int __init lpj_setup(char *str) { preset_lpj = simple_strtoul(str,NULL,0); return 1; }

Contributors

PersonTokensPropCommitsCommitProp
david howellsdavid howells25100.00%1100.00%
Total25100.00%1100.00%

__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 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; unsigned long measured_times[MAX_DIRECT_CALIBRATION_RETRIES]; int max = -1; /* index of measured_times with max/min values or not set */ int min = -1; 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 (time_before_eq(jiffies, start_jiffies + 1)) { pre_start = start; read_current_timer(&start); } read_current_timer(&post_start); pre_end = 0; end = post_start; while (time_before_eq(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 (start >= post_end) printk(KERN_NOTICE "calibrate_delay_direct() ignoring " "timer_rate as we had a TSC wrap around" " start=%lu >=post_end=%lu\n", start, post_end); if (start < post_end && 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; measured_times[i] = timer_rate_max; if (max < 0 || timer_rate_max > measured_times[max]) max = i; if (min < 0 || timer_rate_max < measured_times[min]) min = i; } else measured_times[i] = 0; } /* * Find the maximum & minimum - if they differ too much throw out the * one with the largest difference from the mean and try again... */ while (good_timer_count > 1) { unsigned long estimate; unsigned long maxdiff; /* compute the estimate */ estimate = (good_timer_sum/good_timer_count); maxdiff = estimate >> 3; /* if range is within 12% let's take it */ if ((measured_times[max] - measured_times[min]) < maxdiff) return estimate; /* ok - drop the worse value and try again... */ good_timer_sum = 0; good_timer_count = 0; if ((measured_times[max] - estimate) < (estimate - measured_times[min])) { printk(KERN_NOTICE "calibrate_delay_direct() dropping " "min bogoMips estimate %d = %lu\n", min, measured_times[min]); measured_times[min] = 0; min = max; } else { printk(KERN_NOTICE "calibrate_delay_direct() dropping " "max bogoMips estimate %d = %lu\n", max, measured_times[max]); measured_times[max] = 0; max = min; } for (i = 0; i < MAX_DIRECT_CALIBRATION_RETRIES; i++) { if (measured_times[i] == 0) continue; good_timer_count++; good_timer_sum += measured_times[i]; if (measured_times[i] < measured_times[min]) min = i; if (measured_times[i] > measured_times[max]) max = i; } } printk(KERN_NOTICE "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; }

Contributors

PersonTokensPropCommitsCommitProp
andrew worsleyandrew worsley28855.60%125.00%
venkatesh pallipadivenkatesh pallipadi20639.77%125.00%
alok katariaalok kataria163.09%125.00%
tim deegantim deegan81.54%125.00%
Total518100.00%4100.00%

#else
static unsigned long calibrate_delay_direct(void) { return 0; }

Contributors

PersonTokensPropCommitsCommitProp
venkatesh pallipadivenkatesh pallipadi12100.00%1100.00%
Total12100.00%1100.00%

#endif /* * This is the number of bits of precision for the loops_per_jiffy. Each * 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 * the cpu frequency, hence do the calibration for those. */ #define LPS_PREC 8
static unsigned long calibrate_delay_converge(void) { /* First stage - slowly accelerate to find initial bounds */ unsigned long lpj, lpj_base, ticks, loopadd, loopadd_base, chop_limit; int trials = 0, band = 0, trial_in_band = 0; lpj = (1<<12); /* 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_base = lpj * band; lpj_base = lpj * trials; recalibrate: lpj = lpj_base; loopadd = loopadd_base; /* * Do a binary approximation to get lpj set to * equal one clock (up to LPS_PREC bits) */ chop_limit = lpj >> LPS_PREC; while (loopadd > chop_limit) { lpj += loopadd; ticks = jiffies; while (ticks == jiffies) ; /* nothing */ ticks = jiffies; __delay(lpj); if (jiffies != ticks) /* longer than 1 tick */ lpj -= loopadd; loopadd >>= 1; } /* * If we incremented every single time possible, presume we've * massively underestimated initially, and retry with a higher * start, and larger range. (Only seen on x86_64, due to SMIs) */ if (lpj + loopadd * 2 == lpj_base + loopadd_base * 2) { lpj_base = lpj; loopadd_base <<= 2; goto recalibrate; } return lpj; }

Contributors

PersonTokensPropCommitsCommitProp
phil carmodyphil carmody13964.06%375.00%
david howellsdavid howells7835.94%125.00%
Total217100.00%4100.00%

static DEFINE_PER_CPU(unsigned long, cpu_loops_per_jiffy) = { 0 }; /* * Check if cpu calibration delay is already known. For example, * some processors with multi-core sockets may have all cores * with the same calibration delay. * * Architectures should override this function if a faster calibration * method is available. */ unsigned long __attribute__((weak)) calibrate_delay_is_known(void) { return 0; } /* * Indicate the cpu delay calibration is done. This can be used by * architectures to stop accepting delay timer registrations after this point. */ void __attribute__((weak)) calibration_delay_done(void) { }
void calibrate_delay(void) { unsigned long lpj; static bool printed; int this_cpu = smp_processor_id(); if (per_cpu(cpu_loops_per_jiffy, this_cpu)) { lpj = per_cpu(cpu_loops_per_jiffy, this_cpu); if (!printed) pr_info("Calibrating delay loop (skipped) " "already calibrated this CPU"); } else if (preset_lpj) { lpj = preset_lpj; if (!printed) pr_info("Calibrating delay loop (skipped) " "preset value.. "); } else if ((!printed) && lpj_fine) { lpj = lpj_fine; pr_info("Calibrating delay loop (skipped), " "value calculated using timer frequency.. "); } else if ((lpj = calibrate_delay_is_known())) { ; } else if ((lpj = calibrate_delay_direct()) != 0) { if (!printed) pr_info("Calibrating delay using timer " "specific routine.. "); } else { if (!printed) pr_info("Calibrating delay loop... "); lpj = calibrate_delay_converge(); } per_cpu(cpu_loops_per_jiffy, this_cpu) = lpj; if (!printed) pr_cont("%lu.%02lu BogoMIPS (lpj=%lu)\n", lpj/(500000/HZ), (lpj/(5000/HZ)) % 100, lpj); loops_per_jiffy = lpj; printed = true; calibration_delay_done(); }

Contributors

PersonTokensPropCommitsCommitProp
phil carmodyphil carmody9144.61%111.11%
sameer nandasameer nanda4220.59%111.11%
david howellsdavid howells2411.76%111.11%
russell kingrussell king157.35%111.11%
jack steinerjack steiner136.37%111.11%
mike travismike travis104.90%111.11%
diwakar tundlamdiwakar tundlam52.45%111.11%
peter de schrijverpeter de schrijver31.47%111.11%
alok katariaalok kataria10.49%111.11%
Total204100.00%9100.00%


Overall Contributors

PersonTokensPropCommitsCommitProp
andrew worsleyandrew worsley28826.82%15.88%
venkatesh pallipadivenkatesh pallipadi23621.97%15.88%
phil carmodyphil carmody23121.51%317.65%
david howellsdavid howells15114.06%15.88%
sameer nandasameer nanda575.31%15.88%
jack steinerjack steiner312.89%15.88%
alok katariaalok kataria242.23%211.76%
peter de schrijverpeter de schrijver161.49%15.88%
russell kingrussell king151.40%15.88%
mike travismike travis100.93%15.88%
tim deegantim deegan80.74%15.88%
diwakar tundlamdiwakar tundlam50.47%15.88%
andrew mortonandrew morton10.09%15.88%
tim schmielautim schmielau10.09%15.88%
Total1074100.00%17100.00%
Directory: init
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