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![Randy Dunlap](/assets/img/avatar_default.png)
Optionally add a boot delay after each kernel printk() call, crudely measured in milliseconds, with a maximum delay of 10 seconds per printk. Enable CONFIG_BOOT_PRINTK_DELAY=y and then add (e.g.): "lpj=loops_per_jiffy boot_delay=100" to the kernel command line. It has been useful in cases like "during boot, my machine just reboots or the screen goes black" by slowing down printk, (and adding initcall_debug), we can usually see the last thing that happened before the lights went out which is usually a valuable clue. [akpm@linux-foundation.org: not all architectures implement CONFIG_HZ] [akpm@linux-foundation.org: fix lots of stuff] [bunk@stusta.de: kernel/printk.c: make 2 variables static] [heiko.carstens@de.ibm.com: fix slow down printk on boot compile error] Signed-off-by: Randy Dunlap <rdunlap@xenotime.net> Signed-off-by: Dave Jones <davej@redhat.com> Signed-off-by: Adrian Bunk <bunk@stusta.de> Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
173 lines
4.7 KiB
C
173 lines
4.7 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 <asm/timex.h>
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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 __devinit 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 tsc_rate_min, tsc_rate_max;
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unsigned long good_tsc_sum = 0;
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unsigned long good_tsc_count = 0;
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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 (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 (jiffies <=
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(start_jiffies + 1 + 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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tsc_rate_max = (post_end - pre_start) / DELAY_CALIBRATION_TICKS;
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tsc_rate_min = (pre_end - post_start) / DELAY_CALIBRATION_TICKS;
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/*
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* If the upper limit and lower limit of the tsc_rate is
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* >= 12.5% apart, redo calibration.
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*/
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if (pre_start != 0 && pre_end != 0 &&
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(tsc_rate_max - tsc_rate_min) < (tsc_rate_max >> 3)) {
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good_tsc_count++;
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good_tsc_sum += tsc_rate_max;
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}
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}
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if (good_tsc_count)
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return (good_tsc_sum/good_tsc_count);
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printk(KERN_WARNING "calibrate_delay_direct() failed to get a good "
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"estimate for loops_per_jiffy.\nProbably due to long platform 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 __devinit calibrate_delay_direct(void) {return 0;}
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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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* bit takes on average 1.5/HZ seconds. This (like the original) is a little
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* better than 1%
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*/
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#define LPS_PREC 8
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void __devinit calibrate_delay(void)
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{
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unsigned long ticks, loopbit;
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int lps_precision = LPS_PREC;
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if (preset_lpj) {
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loops_per_jiffy = preset_lpj;
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printk("Calibrating delay loop (skipped)... "
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"%lu.%02lu BogoMIPS preset\n",
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loops_per_jiffy/(500000/HZ),
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(loops_per_jiffy/(5000/HZ)) % 100);
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} else if ((loops_per_jiffy = calibrate_delay_direct()) != 0) {
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printk("Calibrating delay using timer specific routine.. ");
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printk("%lu.%02lu BogoMIPS (lpj=%lu)\n",
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loops_per_jiffy/(500000/HZ),
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(loops_per_jiffy/(5000/HZ)) % 100,
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loops_per_jiffy);
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} else {
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loops_per_jiffy = (1<<12);
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printk(KERN_DEBUG "Calibrating delay loop... ");
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while ((loops_per_jiffy <<= 1) != 0) {
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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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__delay(loops_per_jiffy);
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ticks = jiffies - ticks;
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if (ticks)
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break;
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}
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/*
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* Do a binary approximation to get loops_per_jiffy set to
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* equal one clock (up to lps_precision bits)
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*/
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loops_per_jiffy >>= 1;
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loopbit = loops_per_jiffy;
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while (lps_precision-- && (loopbit >>= 1)) {
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loops_per_jiffy |= loopbit;
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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(loops_per_jiffy);
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if (jiffies != ticks) /* longer than 1 tick */
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loops_per_jiffy &= ~loopbit;
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}
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/* Round the value and print it */
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printk("%lu.%02lu BogoMIPS (lpj=%lu)\n",
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loops_per_jiffy/(500000/HZ),
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(loops_per_jiffy/(5000/HZ)) % 100,
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loops_per_jiffy);
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}
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}
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