* Copyright (C) 1991, 1992 Linus Torvalds
*/
-#include <linux/sched.h>
+#include <linux/jiffies.h>
#include <linux/delay.h>
#include <linux/init.h>
+#include <linux/timex.h>
+#include <linux/smp.h>
-static unsigned long preset_lpj;
+unsigned long lpj_fine;
+unsigned long preset_lpj;
static int __init lpj_setup(char *str)
{
preset_lpj = simple_strtoul(str,NULL,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 __cpuinit 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;
+ 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 (jiffies <= (start_jiffies + 1)) {
+ pre_start = start;
+ read_current_timer(&start);
+ }
+ read_current_timer(&post_start);
+
+ pre_end = 0;
+ end = post_start;
+ while (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 (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;
+ }
+ }
+
+ if (good_timer_count)
+ return (good_timer_sum/good_timer_count);
+
+ printk(KERN_WARNING "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;
+}
+#else
+static unsigned long __cpuinit calibrate_delay_direct(void) {return 0;}
+#endif
+
/*
* This is the number of bits of precision for the loops_per_jiffy. Each
* bit takes on average 1.5/HZ seconds. This (like the original) is a little
* better than 1%
+ * 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
-void __devinit calibrate_delay(void)
+void __cpuinit calibrate_delay(void)
{
unsigned long ticks, loopbit;
int lps_precision = LPS_PREC;
+ static bool printed;
if (preset_lpj) {
loops_per_jiffy = preset_lpj;
- printk("Calibrating delay loop (skipped)... "
- "%lu.%02lu BogoMIPS preset\n",
- loops_per_jiffy/(500000/HZ),
- (loops_per_jiffy/(5000/HZ)) % 100);
+ if (!printed)
+ pr_info("Calibrating delay loop (skipped) "
+ "preset value.. ");
+ } else if ((!printed) && lpj_fine) {
+ loops_per_jiffy = lpj_fine;
+ pr_info("Calibrating delay loop (skipped), "
+ "value calculated using timer frequency.. ");
+ } else if ((loops_per_jiffy = calibrate_delay_direct()) != 0) {
+ if (!printed)
+ pr_info("Calibrating delay using timer "
+ "specific routine.. ");
} else {
loops_per_jiffy = (1<<12);
- printk(KERN_DEBUG "Calibrating delay loop... ");
+ if (!printed)
+ pr_info("Calibrating delay loop... ");
while ((loops_per_jiffy <<= 1) != 0) {
/* wait for "start of" clock tick */
ticks = jiffies;
if (jiffies != ticks) /* longer than 1 tick */
loops_per_jiffy &= ~loopbit;
}
-
- /* Round the value and print it */
- printk("%lu.%02lu BogoMIPS (lpj=%lu)\n",
- loops_per_jiffy/(500000/HZ),
- (loops_per_jiffy/(5000/HZ)) % 100,
- loops_per_jiffy);
}
+ if (!printed)
+ pr_cont("%lu.%02lu BogoMIPS (lpj=%lu)\n",
+ loops_per_jiffy/(500000/HZ),
+ (loops_per_jiffy/(5000/HZ)) % 100, loops_per_jiffy);
+ printed = true;
}
git://ftp.safe.ca / safe / jmp / linux-2.6 / blobdiff