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![Paul Gortmaker](/assets/img/avatar_default.png)
The __cpuinit type of throwaway sections might have made sense
some time ago when RAM was more constrained, but now the savings
do not offset the cost and complications. For example, the fix in
commit 5e427ec2d0
("x86: Fix bit corruption at CPU resume time")
is a good example of the nasty type of bugs that can be created
with improper use of the various __init prefixes.
After a discussion on LKML[1] it was decided that cpuinit should go
the way of devinit and be phased out. Once all the users are gone,
we can then finally remove the macros themselves from linux/init.h.
This removes all the uses of the __cpuinit macros from C files in
the core kernel directories (kernel, init, lib, mm, and include)
that don't really have a specific maintainer.
[1] https://lkml.org/lkml/2013/5/20/589
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
304 lines
8.3 KiB
C
304 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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