Hello,
I implemented GENERIC_TIME and GENERIC_CLOCKEVENTS for
arch-arm/mach-ns9xxx (patches available at
http://www.modarm9.com/git?p=people/ukleinek/linux-2.6.git;a=shortlog;h=clock
or
git://www.modarm9.com/gitsrc/pub/people/ukleinek/linux-2.6.git
in the clock branch
).
If I enable NO_HZ, the system jerks (I hope this is an understandable
term ...). E.g.
# time find /sys
...
real 1m 19.52s
user 0m 0.18s
sys 0m 0.15s
on a freshly booted machine. The output comes in several hunks with
pausing between them. With no_hz=off, I get approx. the same.
If I have NO_HZ disabled however, I get
# time find /sys
...
real 0m 1.53s
user 0m 0.15s
sys 0m 0.18s
Another thing is, if I press Enter once, the next prompt appears in a
reasonable time. If I press twice in a row the 2nd prompt needs
perceptible longer.
Does someone have a hint for me how to debug (or even solve) this problem?
First I wondered why set_next_event is called twice between two timer
interrupts most of the time. I found out that the timer is programed
for the next tick in any case and if nothing needs the next tick, the
interval is enlarged. I didn't spend time yet to check if it is
easier/faster to only program the timer once.
Best regards
Uwe
Some addional data:
- ns9xxx_cpuclock() returns 176947200 = 0xa8c0000 for that machine.
- SYS_TR is a read-only register indicating the current timer value.
- SYS_TRC is the start value (and the reload value for auto-reloading
timers)
- My console is an 8250 clone.
- /proc/timer_list
Timer List Version: v0.3
HRTIMER_MAX_CLOCK_BASES: 2
now at 15091350847 nsecs
cpu: 0
clock 0:
.index: 0
.resolution: 1 nsecs
.get_time: ktime_get_real
.offset: 0 nsecs
active timers:
clock 1:
.index: 1
.resolution: 1 nsecs
.get_time: ktime_get
.offset: 0 nsecs
active timers:
#0: <c02e5ea0>, tick_sched_timer, S:01
# expires at 15100000000 nsecs [in 8649153 nsecs]
.expires_next : 15100000000 nsecs
.hres_active : 1
.nr_events : 424
.nohz_mode : 2
.idle_tick : 14320000000 nsecs
.tick_stopped : 0
.idle_jiffies : 4294938728
.idle_calls : 104
.idle_sleeps : 88
.idle_entrytime : 15052376577 nsecs
.idle_sleeptime : 10627230732 nsecs
.last_jiffies : 4294938801
.next_jiffies : 4294938802
.idle_expires : 15060000000 nsecs
jiffies: 4294938805
Tick Device: mode: 1
Clock Event Device: ns9xxx-timer2
max_delta_ns: 2147483647
min_delta_ns: 1000
mult: 185542
shift: 20
mode: 3
next_event: 15100000000 nsecs
set_next_event: ns9xxx_clockevent_setnextevent
set_mode: ns9xxx_clockevent_setmode
event_handler: hrtimer_interrupt
--
Uwe Kleine-König
http://www.google.com/search?q=e+%5E+%28i+pi%29
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