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Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
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123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145146147148149150151152153154155156157158159160161162163164165166167168169170171172173174175176177178179180181182183184185186187188189190191192193194195196197198199200201202203204205206207208209210211212213214215216217218219220221222223224225226227228229230231232233234235236237238239240241242243244245246247248249250251252253254255256257258259260261262263264265266267268269270271272273274275276277278279280281282283284285286287288289290291292293294295296297298299300301302303304305306307308309310311312313314315316317318319320// SPDX-License-Identifier: GPL-2.0/* calibrate.c: default delay calibration * * Excised from init/main.c * Copyright (C) 1991, 1992 Linus Torvalds */
#include <linux/delay.h>#include <linux/init.h>#include <linux/jiffies.h>#include <linux/kstrtox.h>#include <linux/percpu.h>#include <linux/printk.h>#include <linux/smp.h>#include <linux/stddef.h>#include <linux/timex.h>
unsigned long lpj_fine;unsigned long preset_lpj;
static int __init lpj_setup(char *str){ return kstrtoul(str, 0, &preset_lpj) == 0;}
__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;}#elsestatic 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();}