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Diffstat (limited to 'init/calibrate.c')
| -rw-r--r-- | init/calibrate.c | 316 |
1 files changed, 316 insertions, 0 deletions
diff --git a/init/calibrate.c b/init/calibrate.c new file mode 100644 index 000000000..f3831272f --- /dev/null +++ b/init/calibrate.c @@ -0,0 +1,316 @@ +// SPDX-License-Identifier: GPL-2.0 +/* 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; +} + +__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; +} +#else +static unsigned long calibrate_delay_direct(void) +{ + return 0; +} +#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; +} + +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(); +} |