Hello,
I'm working on a Cortex A9 based platform.
I have a basic clock tree, and a very basic cpufreq driver using
mostly generic driver glue:
static struct cpufreq_driver tangox_cpufreq_driver = {
.name = "tangox-cpufreq",
.init = tangox_cpu_init,
.verify = cpufreq_generic_frequency_table_verify,
.target_index = tangox_target,
.get = cpufreq_generic_get,
.exit = cpufreq_generic_exit,
.attr = cpufreq_generic_attr,
};
My target_index function is trivial:
static int tangox_target(struct cpufreq_policy *policy, unsigned int idx)
{
return clk_set_rate(policy->clk, freq_table[idx].frequency * 1000);
}
I was testing an unrelated driver at low frequencies, with the nominal
frequency (999 MHz) divided by 54 (i.e. freq = 18.5 MHz) and I noticed
that when the driver calls
schedule_timeout(HZ);
the thread sleeps 54 seconds instead of 1.
[ 1107.827279] Sleep for 300 jiffies.
[ 1161.838513] Done sleeping.
(I have HZ set to 300)
I enabled DEBUG in the generic cpufreq driver to see what happens
when I request a frequency change:
# cd /sys/devices/system/cpu/cpu0/cpufreq
# cat scaling_governor
performance
# cat scaling_available_frequencies
999000 499500 333000 199800 111000 18500
# echo 18500 > scaling_max_freq
[ 19.597257] cpufreq: setting new policy for CPU 0: 18500 - 18500 kHz
[ 19.604017] cpufreq: new min and max freqs are 18500 - 18500 kHz
[ 19.610345] cpufreq: governor: change or update limits
[ 19.615596] cpufreq: __cpufreq_governor for CPU 0, event 3
[ 19.621186] cpufreq: target for CPU 0: 18500 kHz, relation 1, requested 18500 kHz
[ 19.628783] cpufreq: __cpufreq_driver_target: cpu: 0, oldfreq: 999000, new freq: 18500
[ 19.636818] cpufreq: notification 0 of frequency transition to 18500 kHz
[ 19.643625] cpufreq: notification 0 of frequency transition to 18500 kHz
[ 19.650454] NEW RATE=9250000
[ 19.653644] NEW RATE=9250000
[ 19.657091] cpufreq: notification 1 of frequency transition to 18500 kHz
[ 19.664176] cpufreq: FREQ: 18500 - CPU: 0
[ 19.668412] cpufreq: notification 1 of frequency transition to 18500 kHz
[ 19.675648] cpufreq: FREQ: 18500 - CPU: 1
The "NEW RATE" traces are ones I added in smp_twd.c:twd_update_frequency()
(my clockevent source) to check whether the CPU frequency change propagated
to smp_twd.
I must have made an obvious mistake. Could someone point it out to me?
(I have attached the output of /proc/timer_list to this message)
Looking more closely at schedule_timeout(), I suppose the work happens
in __mod_timer()... Hmm, that one is over my head.
What am I missing?
Regards.
Timer List Version: v0.7
HRTIMER_MAX_CLOCK_BASES: 4
now at 1996236245543 nsecs
cpu: 0
clock 0:
.base: e7ae51e8
.index: 0
.resolution: 3333333 nsecs
.get_time: ktime_get
.offset: 0 nsecs
active timers:
#0: sched_clock_timer, sched_clock_poll, S:01
# expires at 2087831315985-2087831315985 nsecs [in 91595070442 to 91595070442 nsecs]
clock 1:
.base: e7ae5220
.index: 1
.resolution: 3333333 nsecs
.get_time: ktime_get_real
.offset: 0 nsecs
active timers:
clock 2:
.base: e7ae5258
.index: 2
.resolution: 3333333 nsecs
.get_time: ktime_get_boottime
.offset: 0 nsecs
active timers:
clock 3:
.base: e7ae5290
.index: 3
.resolution: 3333333 nsecs
.get_time: ktime_get_clocktai
.offset: 0 nsecs
active timers:
.expires_next : 9223372036854775807 nsecs
.hres_active : 0
.nr_events : 0
.nr_retries : 0
.nr_hangs : 0
.max_hang_time : 0 nsecs
.nohz_mode : 0
.last_tick : 0 nsecs
.tick_stopped : 0
.idle_jiffies : 0
.idle_calls : 0
.idle_sleeps : 0
.idle_entrytime : 1996229420769 nsecs
.idle_waketime : 0 nsecs
.idle_exittime : 0 nsecs
.idle_sleeptime : 1985388003747 nsecs
.iowait_sleeptime: 10995516 nsecs
.last_jiffies : 0
.next_jiffies : 0
.idle_expires : 0 nsecs
jiffies: 4294894041
cpu: 1
clock 0:
.base: e7aed1e8
.index: 0
.resolution: 3333333 nsecs
.get_time: ktime_get
.offset: 0 nsecs
active timers:
clock 1:
.base: e7aed220
.index: 1
.resolution: 3333333 nsecs
.get_time: ktime_get_real
.offset: 0 nsecs
active timers:
clock 2:
.base: e7aed258
.index: 2
.resolution: 3333333 nsecs
.get_time: ktime_get_boottime
.offset: 0 nsecs
active timers:
clock 3:
.base: e7aed290
.index: 3
.resolution: 3333333 nsecs
.get_time: ktime_get_clocktai
.offset: 0 nsecs
active timers:
.expires_next : 9223372036854775807 nsecs
.hres_active : 0
.nr_events : 0
.nr_retries : 0
.nr_hangs : 0
.max_hang_time : 0 nsecs
.nohz_mode : 0
.last_tick : 0 nsecs
.tick_stopped : 0
.idle_jiffies : 0
.idle_calls : 0
.idle_sleeps : 0
.idle_entrytime : 1996231929568 nsecs
.idle_waketime : 0 nsecs
.idle_exittime : 0 nsecs
.idle_sleeptime : 1992784761637 nsecs
.iowait_sleeptime: 40375788 nsecs
.last_jiffies : 0
.next_jiffies : 0
.idle_expires : 0 nsecs
jiffies: 4294894041
Tick Device: mode: 0
Broadcast device
Clock Event Device: <NULL>
tick_broadcast_mask: 00000000
tick_broadcast_oneshot_mask: 00000000
Tick Device: mode: 0
Per CPU device: 0
Clock Event Device: local_timer
max_delta_ns: 464320782665
min_delta_ns: 1622
mult: 19864224
shift: 31
mode: 2
next_event: 9223372036854775807 nsecs
set_next_event: twd_set_next_event
set_mode: twd_set_mode
event_handler: tick_handle_periodic
retries: 0
Tick Device: mode: 0
Per CPU device: 1
Clock Event Device: local_timer
max_delta_ns: 464320782665
min_delta_ns: 1622
mult: 19864224
shift: 31
mode: 2
next_event: 9223372036854775807 nsecs
set_next_event: twd_set_next_event
set_mode: twd_set_mode
event_handler: tick_handle_periodic
retries: 0
