X-Git-Url: http://git.onelab.eu/?a=blobdiff_plain;f=init%2Fcalibrate.c;h=733f14b88085830984d1c80382f429921aec9c36;hb=43bc926fffd92024b46cafaf7350d669ba9ca884;hp=4841f3e169496fa0945713bd6c1671fba1b23111;hpb=cee37fe97739d85991964371c1f3a745c00dd236;p=linux-2.6.git

diff --git a/init/calibrate.c b/init/calibrate.c
index 4841f3e16..733f14b88 100644
--- a/init/calibrate.c
+++ b/init/calibrate.c
@@ -8,7 +8,9 @@
 #include <linux/delay.h>
 #include <linux/init.h>
 
-static unsigned long preset_lpj;
+#include <asm/timex.h>
+
+unsigned long preset_lpj;
 static int __init lpj_setup(char *str)
 {
 	preset_lpj = simple_strtoul(str,NULL,0);
@@ -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
@@ -33,8 +121,14 @@ void __devinit calibrate_delay(void)
 		loops_per_jiffy = preset_lpj;
 		printk("Calibrating delay loop (skipped)... "
 			"%lu.%02lu BogoMIPS preset\n",
-			HZ*(loops_per_jiffy >> 3)/62500,
-			(HZ*(loops_per_jiffy >> 3)/625) % 100);
+			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);
 
@@ -71,8 +165,8 @@ void __devinit calibrate_delay(void)
 
 		/* Round the value and print it */
 		printk("%lu.%02lu BogoMIPS (lpj=%lu)\n",
-			HZ*(loops_per_jiffy >> 3)/62500,
-			(HZ*(loops_per_jiffy >> 3)/625) % 100,
+			loops_per_jiffy/(500000/HZ),
+			(loops_per_jiffy/(5000/HZ)) % 100,
 			loops_per_jiffy);
 	}