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-rw-r--r--init/calibrate.c94
1 files changed, 94 insertions, 0 deletions
diff --git a/init/calibrate.c b/init/calibrate.c
index c698e04a3db..d206c7548fe 100644
--- a/init/calibrate.c
+++ b/init/calibrate.c
@@ -8,6 +8,8 @@
#include <linux/delay.h>
#include <linux/init.h>
+#include <asm/timex.h>
+
static unsigned long preset_lpj;
static int __init lpj_setup(char *str)
{
@@ -17,6 +19,92 @@ static int __init lpj_setup(char *str)
__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 __devinit calibrate_delay_direct(void)
+{
+ unsigned long pre_start, start, post_start;
+ unsigned long pre_end, end, post_end;
+ unsigned long start_jiffies;
+ unsigned long tsc_rate_min, tsc_rate_max;
+ unsigned long good_tsc_sum = 0;
+ unsigned long good_tsc_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);
+
+ tsc_rate_max = (post_end - pre_start) / DELAY_CALIBRATION_TICKS;
+ tsc_rate_min = (pre_end - post_start) / DELAY_CALIBRATION_TICKS;
+
+ /*
+ * If the upper limit and lower limit of the tsc_rate is
+ * >= 12.5% apart, redo calibration.
+ */
+ if (pre_start != 0 && pre_end != 0 &&
+ (tsc_rate_max - tsc_rate_min) < (tsc_rate_max >> 3)) {
+ good_tsc_count++;
+ good_tsc_sum += tsc_rate_max;
+ }
+ }
+
+ if (good_tsc_count)
+ return (good_tsc_sum/good_tsc_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 __devinit 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
@@ -35,6 +123,12 @@ void __devinit calibrate_delay(void)
"%lu.%02lu BogoMIPS preset\n",
loops_per_jiffy/(500000/HZ),
(loops_per_jiffy/(5000/HZ)) % 100);
+ } else if ((loops_per_jiffy = calibrate_delay_direct()) != 0) {
+ printk("Calibrating delay using timer specific routine.. ");
+ printk("%lu.%02lu BogoMIPS (lpj=%lu)\n",
+ loops_per_jiffy/(500000/HZ),
+ (loops_per_jiffy/(5000/HZ)) % 100,
+ loops_per_jiffy);
} else {
loops_per_jiffy = (1<<12);