Home
__Skew processor clocks (TSC register) on SMP systems__

**SKEW**: Skew processor clocks (TSC register) on SMP systems
__Syntax:__
skew [-s [#sec]] [-q]
__Where:__
-s Skew the clocks.
* If #sec is specified then clocks are skewed #secs from
each other.
* If #sec is not specified then clocks are skewed 60 secs
(1 min) from each other.
* The highest numbered processor will have the largest skew
(relative to processor 0). Processor 0 will have the smallest
skew.
* Clock skew is displayed at completion of the command.
-q Query clock skew.
* Displays current value of TSC for all processors
and the difference from processor 0's TSC and from the TSC
from the next mumerically lower processor number.
__Notes:__
* Skewing is accomplished by resetting (to 0) the TSC register.
Any code that relies on the TSC not going backwards may have
problems.
* The command won't complete until all clocks are skewed. So, for
example, if you request clocks to be skewed by 2 minutes on an
8-way SMP machine, the command will run for 14 minutes.
* Skew display data fields:
- TSC:
Current value of the TSC
- Delta (CPU0):
Difference in values between this processor and processor 0.
The difference is expressed as an absolute value.
- Delta (prev CPU):
Difference in values between this processor and previous
(numerically lower) processor. The difference is expressed
as an absolute value.
- Time:
Approximate time, in seconds, represented by the cycles value.
May display as 0 (zero) for very small skews.
__Examples:__
1) The following both skew the clocks by 60 seconds:
* skew -s
* skew -s 60
2) Display current clock skew:
- skew -q
3) Sample output on system where clocks are not skewed:
Delta (CPU0) Delta (prev CPU)
TSC Value Cycles Time Cycles Time
------------------- --------------- ---- --------------- ----
CPU0: 0x00000007:8BF43FD8 0x0000:00000000 0.0 0x0000:00000000 0.0
CPU1: 0x00000007:8BF53540 0x0000:0000F568 0.0 0x0000:0000F568 0.0
CPU2: 0x00000007:8BF45118 0x0000:00001140 0.0 0x0000:0000E428 0.0
CPU3: 0x00000007:8BF554F8 0x0000:00011520 0.0 0x0000:000103E0 0.0
4) Sample output on system where clocks are skewed:
Delta (CPU0) Delta (prev CPU)
TSC Value Cycles Time Cycles Time
------------------- --------------- ---- --------------- ----
CPU0: 0x00000000:000198E8 0x0000:00000000 0.0 0x0000:00000000 0.0
CPU1: 0x0000000D:F0650204 0x000D:F063691C 25.0 0x000D:F063691C 25.0
CPU2: 0x0000001B:E0C43A30 0x001B:E0C2A148 50.0 0x000D:F05F382C 25.0
CPU3: 0x00000029:D09D62AC 0x0029:D09BC9C4 75.0 0x000D:EFD9287C 25.0

Home