Hi all,
I was trying to make sense of the data that I collected earlier with the
idle1.stp probe. It displayed the percentage of time spent in halted mode, which
the highest I saw on an idle machine was 17 percentage. This seemed rather low
for a machine that was doing nothing, so I took a closer look at what was going
on the idle machine. All this work is based on kernel built from dilinger's:
kernel-2.6.21-20070312.1.olpc.3eca75102a57502.src.rpm
I ran an experiment where the machine state idle for 10 seconds with the
systemtap script running. I also compared the number of interrupts before and
after the experiment. There is about 150 interrupts per second from the mfgpt
timer. I thought with the tickless kernel that this would be a lot lower.
Below is the data from the experiment. I tried booting the machine in runlevel
three and got the same results, about 150 interrupts per second. Why so many
timer interrupts for tickless kernel?
-Will
cat /proc/interrupts > /tmp/tone; staprun idle1.ko -c 'sleep 10'; cat
/proc/interrupts > /tmp/tten; diff -u /tmp/tone /tmp/tten
Starting halt watch
Ran for 10117637 us
entered default_halt 1619
exited default_halt 1619
percent halted: 17
count: 1619
avg_time: 1083
min_time: 3
max_time: 2553
usec distribution
value |-------------------------------------------------- count
0 | 0
1 | 0
2 | 1
4 | 18
8 | 19
16 |@ 26
32 |@ 37
64 |@ 48
128 |@ 37
256 |@ 51
512 |@@@ 97
1024 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ 1284
2048 | 1
4096 | 0
8192 | 0
--- /tmp/tone 2007-03-22 13:37:38.931938793 -0400
+++ /tmp/tten 2007-03-22 13:37:49.932104719 -0400
@@ -6,9 +6,9 @@
4: 12 XT-PIC-XT serial
5: 0 XT-PIC-XT CS5535 Audio
6: 0 XT-PIC-XT DCON
- 7: 222470 XT-PIC-XT mfgpt-timer
+ 7: 224002 XT-PIC-XT mfgpt-timer
8: 1 XT-PIC-XT rtc
- 10: 93831 XT-PIC-XT ehci_hcd:usb1, ohci_hcd:usb2
+ 10: 94187 XT-PIC-XT ehci_hcd:usb1, ohci_hcd:usb2
11: 162 XT-PIC-XT CAFE NAND, cafe-ccic, sdhci:slot0
12: 97 XT-PIC-XT i8042
NMI: 0
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