x86: use cpu_khz for loops_per_jiffy calculation
Alok Kataria [Fri, 20 Jun 2008 22:06:33 +0000 (15:06 -0700)]
On the x86 platform we can use the value of tsc_khz computed during tsc
calibration to calculate the loops_per_jiffy value. Its very important
to keep the error in lpj values to minimum as any error in that may
result in kernel panic in check_timer. In virtualization environment, On
a highly overloaded host the guest delay calibration may sometimes
result in errors beyond the ~50% that timer_irq_works can handle,
resulting in the guest panicking.

Does some formating changes to lpj_setup code to now have a single
printk to print the bogomips value.

We do this only for the boot processor because the AP's can have
different base frequencies or the BIOS might boot a AP at a different
frequency.

Signed-off-by: Alok N Kataria <akataria@vmware.com>
Cc: Arjan van de Ven <arjan@infradead.org>
Cc: Daniel Hecht <dhecht@vmware.com>
Cc: Tim Mann <mann@vmware.com>
Cc: Zach Amsden <zach@vmware.com>
Cc: Sahil Rihan <srihan@vmware.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/kernel/time_64.c
arch/x86/kernel/tsc_32.c
include/linux/delay.h
init/calibrate.c

index c737849..12b4a71 100644 (file)
@@ -123,6 +123,8 @@ void __init time_init(void)
                (boot_cpu_data.x86_vendor == X86_VENDOR_AMD))
                cpu_khz = calculate_cpu_khz();
 
+       lpj_tsc = ((unsigned long)tsc_khz * 1000)/HZ;
+
        if (unsynchronized_tsc())
                mark_tsc_unstable("TSCs unsynchronized");
 
index 068759d..be72903 100644 (file)
@@ -401,6 +401,7 @@ static inline void check_geode_tsc_reliable(void) { }
 void __init tsc_init(void)
 {
        int cpu;
+       u64 lpj;
 
        if (!cpu_has_tsc || tsc_disabled) {
                /* Disable the TSC in case of !cpu_has_tsc */
@@ -421,6 +422,10 @@ void __init tsc_init(void)
                return;
        }
 
+       lpj = ((u64)tsc_khz * 1000);
+       do_div(lpj, HZ);
+       lpj_tsc = lpj;
+
        printk("Detected %lu.%03lu MHz processor.\n",
                                (unsigned long)cpu_khz / 1000,
                                (unsigned long)cpu_khz % 1000);
index 54552d2..01aec60 100644 (file)
@@ -41,6 +41,7 @@ static inline void ndelay(unsigned long x)
 #define ndelay(x) ndelay(x)
 #endif
 
+extern unsigned long lpj_tsc;
 void calibrate_delay(void);
 void msleep(unsigned int msecs);
 unsigned long msleep_interruptible(unsigned int msecs);
index ecb3822..8628697 100644 (file)
@@ -8,7 +8,9 @@
 #include <linux/delay.h>
 #include <linux/init.h>
 #include <linux/timex.h>
+#include <linux/smp.h>
 
+unsigned long lpj_tsc;
 unsigned long preset_lpj;
 static int __init lpj_setup(char *str)
 {
@@ -108,6 +110,10 @@ static unsigned long __cpuinit calibrate_delay_direct(void) {return 0;}
  * 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 tsc frequency.
+ * For the rest of the CPUs we cannot assume that the tsc frequency is same as
+ * the cpu frequency, hence do the calibration for those.
  */
 #define LPS_PREC 8
 
@@ -118,20 +124,20 @@ void __cpuinit calibrate_delay(void)
 
        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);
+               printk(KERN_INFO
+                       "Calibrating delay loop (skipped) preset value.. ");
+       } else if ((smp_processor_id() == 0) && lpj_tsc) {
+               loops_per_jiffy = lpj_tsc;
+               printk(KERN_INFO
+                       "Calibrating delay loop (skipped), "
+                       "using tsc calculated value.. ");
        } 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);
+               printk(KERN_INFO
+                       "Calibrating delay using timer specific routine.. ");
        } else {
                loops_per_jiffy = (1<<12);
 
-               printk(KERN_DEBUG "Calibrating delay loop... ");
+               printk(KERN_INFO "Calibrating delay loop... ");
                while ((loops_per_jiffy <<= 1) != 0) {
                        /* wait for "start of" clock tick */
                        ticks = jiffies;
@@ -161,12 +167,8 @@ void __cpuinit calibrate_delay(void)
                        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);
        }
-
+       printk(KERN_INFO "%lu.%02lu BogoMIPS (lpj=%lu)\n",
+                       loops_per_jiffy/(500000/HZ),
+                       (loops_per_jiffy/(5000/HZ)) % 100, loops_per_jiffy);
 }