timecounter TSC on Core i7

[Joachim Kuebart <joachim.kuebart%gmx.net@localhost>]

Hi,

I have a problem with NetBSD picking timecounter TSC as the primary time 
source on a Core i7-920 system.

The dmesg shows that the frequency is sometimes detected as 2.6GHz (very 
rarely), while most of the time it's 3.7GHz (see diff below). I'm 
assuming this is due to whether or not Turbo Boost happens to be in 
effect when the kernel boots. Nevertheless, the kernel assigns q=3000 to 
TSC and in most cases (when it detects 3.7GHz) the system clock runs 
very very slowly (compared to wall time).

There is some complicated code in sys/arch/x86/x86/tsc.c to try and 
decide whether TSC can be used reliably, but in my case it seems to get 
it wrong.

I've been running with "sysctl -w kern.timecounter.hardware=hpet0" 
(q=2000) for a while now and it's behaving much better than before. I 
think this should probably be the default for Core i7 systems if this 
isn't supposed to become an FAQ :-)

Best regards,

Joachim


--- ./dmesg.accurateclock       2009-09-08 16:20:59.000000000 +0100
+++ ./dmesg.clockslow   2009-09-07 09:49:39.000000000 +0100
@@ -12,14 +12,14 @@
 timecounter: Timecounter "i8254" frequency 1193182 Hz quality 100
 System manufacturer System Product Name (System Version)
 mainbus0 (root)
-cpu0 at mainbus0 apid 0: Intel 686-class, 2672MHz, id 0x106a5
-cpu1 at mainbus0 apid 2: Intel 686-class, 2672MHz, id 0x106a5
-cpu2 at mainbus0 apid 4: Intel 686-class, 2672MHz, id 0x106a5
-cpu3 at mainbus0 apid 6: Intel 686-class, 2672MHz, id 0x106a5
-cpu4 at mainbus0 apid 1: Intel 686-class, 2672MHz, id 0x106a5
-cpu5 at mainbus0 apid 3: Intel 686-class, 2672MHz, id 0x106a5
-cpu6 at mainbus0 apid 5: Intel 686-class, 2672MHz, id 0x106a5
-cpu7 at mainbus0 apid 7: Intel 686-class, 2672MHz, id 0x106a5
+cpu0 at mainbus0 apid 0: Intel 686-class, 3741MHz, id 0x106a5
+cpu1 at mainbus0 apid 2: Intel 686-class, 3741MHz, id 0x106a5
+cpu2 at mainbus0 apid 4: Intel 686-class, 3741MHz, id 0x106a5
+cpu3 at mainbus0 apid 6: Intel 686-class, 3741MHz, id 0x106a5
+cpu4 at mainbus0 apid 1: Intel 686-class, 3741MHz, id 0x106a5
+cpu5 at mainbus0 apid 3: Intel 686-class, 3741MHz, id 0x106a5
+cpu6 at mainbus0 apid 5: Intel 686-class, 3741MHz, id 0x106a5
+cpu7 at mainbus0 apid 7: Intel 686-class, 3741MHz, id 0x106a5
 ioapic0 at mainbus0 apid 8: pa 0xfec00000, version 20, 24 pins
 ioapic1 at mainbus0 apid 9: pa 0xfec8a000, version 20, 24 pins
 acpi0 at mainbus0: Intel ACPICA 20090730
@@ -170,7 +170,7 @@
 ieee1394if0: 1 nodes, maxhop <= 0, cable IRM = 0 (me)
 ieee1394if0: bus manager 0 (me)
 timecounter: Timecounter "clockinterrupt" frequency 100 Hz quality 0
-timecounter: Timecounter "TSC" frequency 2672861800 Hz quality 3000
+timecounter: Timecounter "TSC" frequency 3741967920 Hz quality 3000
 azalia0: codec[0]: ATI R600 HDMI (rev. 1.0), HDA rev. 1.0
 audio0 at azalia0: full duplex, independent
 azalia1: codec[0]: Realtek ALC888 (rev. 1.1), HDA rev. 1.0