305 lines
8.3 KiB
C
305 lines
8.3 KiB
C
/* calibrate.c: default delay calibration
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*
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* Excised from init/main.c
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* Copyright (C) 1991, 1992 Linus Torvalds
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*/
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#include <linux/jiffies.h>
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#include <linux/delay.h>
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#include <linux/init.h>
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#include <linux/timex.h>
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#include <linux/smp.h>
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#include <linux/percpu.h>
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unsigned long lpj_fine;
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unsigned long preset_lpj;
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static int __init lpj_setup(char *str)
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{
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preset_lpj = simple_strtoul(str,NULL,0);
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return 1;
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}
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__setup("lpj=", lpj_setup);
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#ifdef ARCH_HAS_READ_CURRENT_TIMER
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/* This routine uses the read_current_timer() routine and gets the
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* loops per jiffy directly, instead of guessing it using delay().
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* Also, this code tries to handle non-maskable asynchronous events
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* (like SMIs)
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*/
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#define DELAY_CALIBRATION_TICKS ((HZ < 100) ? 1 : (HZ/100))
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#define MAX_DIRECT_CALIBRATION_RETRIES 5
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static unsigned long calibrate_delay_direct(void)
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{
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unsigned long pre_start, start, post_start;
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unsigned long pre_end, end, post_end;
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unsigned long start_jiffies;
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unsigned long timer_rate_min, timer_rate_max;
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unsigned long good_timer_sum = 0;
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unsigned long good_timer_count = 0;
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unsigned long measured_times[MAX_DIRECT_CALIBRATION_RETRIES];
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int max = -1; /* index of measured_times with max/min values or not set */
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int min = -1;
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int i;
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if (read_current_timer(&pre_start) < 0 )
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return 0;
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/*
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* A simple loop like
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* while ( jiffies < start_jiffies+1)
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* start = read_current_timer();
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* will not do. As we don't really know whether jiffy switch
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* happened first or timer_value was read first. And some asynchronous
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* event can happen between these two events introducing errors in lpj.
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*
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* So, we do
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* 1. pre_start <- When we are sure that jiffy switch hasn't happened
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* 2. check jiffy switch
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* 3. start <- timer value before or after jiffy switch
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* 4. post_start <- When we are sure that jiffy switch has happened
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*
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* Note, we don't know anything about order of 2 and 3.
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* Now, by looking at post_start and pre_start difference, we can
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* check whether any asynchronous event happened or not
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*/
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for (i = 0; i < MAX_DIRECT_CALIBRATION_RETRIES; i++) {
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pre_start = 0;
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read_current_timer(&start);
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start_jiffies = jiffies;
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while (time_before_eq(jiffies, start_jiffies + 1)) {
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pre_start = start;
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read_current_timer(&start);
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}
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read_current_timer(&post_start);
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pre_end = 0;
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end = post_start;
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while (time_before_eq(jiffies, start_jiffies + 1 +
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DELAY_CALIBRATION_TICKS)) {
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pre_end = end;
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read_current_timer(&end);
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}
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read_current_timer(&post_end);
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timer_rate_max = (post_end - pre_start) /
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DELAY_CALIBRATION_TICKS;
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timer_rate_min = (pre_end - post_start) /
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DELAY_CALIBRATION_TICKS;
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/*
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* If the upper limit and lower limit of the timer_rate is
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* >= 12.5% apart, redo calibration.
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*/
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if (start >= post_end)
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printk(KERN_NOTICE "calibrate_delay_direct() ignoring "
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"timer_rate as we had a TSC wrap around"
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" start=%lu >=post_end=%lu\n",
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start, post_end);
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if (start < post_end && pre_start != 0 && pre_end != 0 &&
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(timer_rate_max - timer_rate_min) < (timer_rate_max >> 3)) {
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good_timer_count++;
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good_timer_sum += timer_rate_max;
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measured_times[i] = timer_rate_max;
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if (max < 0 || timer_rate_max > measured_times[max])
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max = i;
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if (min < 0 || timer_rate_max < measured_times[min])
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min = i;
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} else
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measured_times[i] = 0;
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}
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/*
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* Find the maximum & minimum - if they differ too much throw out the
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* one with the largest difference from the mean and try again...
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*/
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while (good_timer_count > 1) {
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unsigned long estimate;
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unsigned long maxdiff;
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/* compute the estimate */
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estimate = (good_timer_sum/good_timer_count);
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maxdiff = estimate >> 3;
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/* if range is within 12% let's take it */
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if ((measured_times[max] - measured_times[min]) < maxdiff)
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return estimate;
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/* ok - drop the worse value and try again... */
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good_timer_sum = 0;
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good_timer_count = 0;
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if ((measured_times[max] - estimate) <
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(estimate - measured_times[min])) {
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printk(KERN_NOTICE "calibrate_delay_direct() dropping "
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"min bogoMips estimate %d = %lu\n",
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min, measured_times[min]);
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measured_times[min] = 0;
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min = max;
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} else {
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printk(KERN_NOTICE "calibrate_delay_direct() dropping "
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"max bogoMips estimate %d = %lu\n",
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max, measured_times[max]);
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measured_times[max] = 0;
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max = min;
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}
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for (i = 0; i < MAX_DIRECT_CALIBRATION_RETRIES; i++) {
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if (measured_times[i] == 0)
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continue;
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good_timer_count++;
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good_timer_sum += measured_times[i];
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if (measured_times[i] < measured_times[min])
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min = i;
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if (measured_times[i] > measured_times[max])
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max = i;
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}
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}
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printk(KERN_NOTICE "calibrate_delay_direct() failed to get a good "
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"estimate for loops_per_jiffy.\nProbably due to long platform "
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"interrupts. Consider using \"lpj=\" boot option.\n");
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return 0;
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}
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#else
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static unsigned long calibrate_delay_direct(void)
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{
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return 0;
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}
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#endif
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/*
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* This is the number of bits of precision for the loops_per_jiffy. Each
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* time we refine our estimate after the first takes 1.5/HZ seconds, so try
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* to start with a good estimate.
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* For the boot cpu we can skip the delay calibration and assign it a value
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* calculated based on the timer frequency.
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* For the rest of the CPUs we cannot assume that the timer frequency is same as
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* the cpu frequency, hence do the calibration for those.
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*/
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#define LPS_PREC 8
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static unsigned long calibrate_delay_converge(void)
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{
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/* First stage - slowly accelerate to find initial bounds */
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unsigned long lpj, lpj_base, ticks, loopadd, loopadd_base, chop_limit;
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int trials = 0, band = 0, trial_in_band = 0;
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lpj = (1<<12);
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/* wait for "start of" clock tick */
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ticks = jiffies;
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while (ticks == jiffies)
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; /* nothing */
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/* Go .. */
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ticks = jiffies;
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do {
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if (++trial_in_band == (1<<band)) {
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++band;
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trial_in_band = 0;
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}
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__delay(lpj * band);
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trials += band;
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} while (ticks == jiffies);
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/*
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* We overshot, so retreat to a clear underestimate. Then estimate
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* the largest likely undershoot. This defines our chop bounds.
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*/
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trials -= band;
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loopadd_base = lpj * band;
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lpj_base = lpj * trials;
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recalibrate:
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lpj = lpj_base;
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loopadd = loopadd_base;
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/*
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* Do a binary approximation to get lpj set to
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* equal one clock (up to LPS_PREC bits)
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*/
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chop_limit = lpj >> LPS_PREC;
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while (loopadd > chop_limit) {
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lpj += loopadd;
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ticks = jiffies;
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while (ticks == jiffies)
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; /* nothing */
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ticks = jiffies;
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__delay(lpj);
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if (jiffies != ticks) /* longer than 1 tick */
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lpj -= loopadd;
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loopadd >>= 1;
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}
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/*
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* If we incremented every single time possible, presume we've
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* massively underestimated initially, and retry with a higher
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* start, and larger range. (Only seen on x86_64, due to SMIs)
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*/
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if (lpj + loopadd * 2 == lpj_base + loopadd_base * 2) {
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lpj_base = lpj;
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loopadd_base <<= 2;
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goto recalibrate;
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}
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return lpj;
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}
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static DEFINE_PER_CPU(unsigned long, cpu_loops_per_jiffy) = { 0 };
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/*
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* Check if cpu calibration delay is already known. For example,
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* some processors with multi-core sockets may have all cores
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* with the same calibration delay.
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*
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* Architectures should override this function if a faster calibration
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* method is available.
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*/
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unsigned long __attribute__((weak)) calibrate_delay_is_known(void)
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{
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return 0;
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}
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void calibrate_delay(void)
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{
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unsigned long lpj;
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static bool printed;
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int this_cpu = smp_processor_id();
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if (per_cpu(cpu_loops_per_jiffy, this_cpu)) {
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lpj = per_cpu(cpu_loops_per_jiffy, this_cpu);
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if (!printed)
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pr_info("Calibrating delay loop (skipped) "
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"already calibrated this CPU");
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} else if (preset_lpj) {
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lpj = preset_lpj;
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if (!printed)
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pr_info("Calibrating delay loop (skipped) "
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"preset value.. ");
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} else if ((!printed) && lpj_fine) {
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lpj = lpj_fine;
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pr_info("Calibrating delay loop (skipped), "
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"value calculated using timer frequency.. ");
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} else if ((lpj = calibrate_delay_is_known())) {
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;
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} else if ((lpj = calibrate_delay_direct()) != 0) {
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if (!printed)
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pr_info("Calibrating delay using timer "
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"specific routine.. ");
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} else {
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if (!printed)
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pr_info("Calibrating delay loop... ");
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lpj = calibrate_delay_converge();
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}
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per_cpu(cpu_loops_per_jiffy, this_cpu) = lpj;
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if (!printed)
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pr_cont("%lu.%02lu BogoMIPS (lpj=%lu)\n",
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lpj/(500000/HZ),
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(lpj/(5000/HZ)) % 100, lpj);
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loops_per_jiffy = lpj;
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printed = true;
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}
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