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316 lines
8.6 KiB
316 lines
8.6 KiB
// SPDX-License-Identifier: GPL-2.0 |
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/* 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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/* |
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* Indicate the cpu delay calibration is done. This can be used by |
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* architectures to stop accepting delay timer registrations after this point. |
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*/ |
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void __attribute__((weak)) calibration_delay_done(void) |
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{ |
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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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calibration_delay_done(); |
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}
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