Thomas,

I just was wondering how the HR Timers were in the latest -rtX patch and
wrote my own little jitter test using nanosleep.  Here's the results:

On vanilla 2.6.13-rc7-git1  (Yes I need to get over to 2.6.13)

# ./jitter
starting calibrate
finished calibrate: 2133.9060MHz 2133906034
time slept: 0.010000000 sec: 0 nsec: 10000000
max: 0.011997701
min: 0.011890522
avg: 0.011993485
greatest time over: 1997.701 usecs
never ran under (good!)
average time over: 1993.485 usecs

On 2.6.13-rt3:

# ./jitter
starting calibrate
finished calibrate: 2133.2960MHz 2133295991
time slept: 0.010000000 sec: 0 nsec: 10000000
max: 0.010034857
min: 0.010006309
avg: 0.010009213
greatest time over: 34.857 usecs
never ran under (good!)
average time over: 9.213 usecs


Not bad.  I then ran a clean kernel compile as root with a -j3 (this is
an 2x SMP machine), and tried the test again.

# ./jitter
starting calibrate
finished calibrate: 2133.3005MHz 2133300491
time slept: 0.010000000 sec: 0 nsec: 10000000
max: 0.010044836
min: 0.010014244
avg: 0.010030741
greatest time over: 44.836 usecs
never ran under (good!)
average time over: 30.741 usecs


Since the ticks per second is also calculated here, I ran it again using
the calibration of the first run (still running that make):

./jitter -c 2133295991
passed in calibrate: 2133.2960MHz 2133295991
time slept: 0.010000000 sec: 0 nsec: 10000000
max: 0.010051293
min: 0.010012155
avg: 0.010030237
greatest time over: 51.293 usecs
never ran under (good!)
average time over: 30.237 usecs

And once more using the calibration found by 2.6.13-rc7-git1 (still
running that make):

# ./jitter -c 2133906034
passed in calibrate: 2133.9060MHz 2133906034
time slept: 0.010000000 sec: 0 nsec: 10000000
max: 0.010058339
min: 0.010016418
avg: 0.010025571
greatest time over: 58.339 usecs
never ran under (good!)
average time over: 25.571 usecs


Some info on my machine:

$ cat /proc/cpuinfo
processor       : 0
vendor_id       : AuthenticAMD
cpu family      : 6
model           : 10
model name      : AMD Athlon(tm) MP 2800+
stepping        : 0
cpu MHz         : 2133.286
cache size      : 512 KB
fdiv_bug        : no
hlt_bug         : no
f00f_bug        : no
coma_bug        : no
fpu             : yes
fpu_exception   : yes
cpuid level     : 1
wp              : yes
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge
mca cmov pat pse36 mmx fxsr sse syscall mp mmxext 3dnowext 3dnow
bogomips        : 4259.84

processor       : 1
vendor_id       : AuthenticAMD
cpu family      : 6
model           : 10
model name      : AMD Athlon(tm) Processor
stepping        : 0
cpu MHz         : 2133.286
cache size      : 512 KB
fdiv_bug        : no
hlt_bug         : no
f00f_bug        : no
coma_bug        : no
fpu             : yes
fpu_exception   : yes
cpuid level     : 1
wp              : yes
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge
mca cmov pat pse36 mmx fxsr sse syscall mp mmxext 3dnowext 3dnow
bogomips        : 4259.84

And attached is the jitter.c test. Must be run as root since it ups the
priority to the max.

Have fun,

-- Steve