On Wednesday 14 April 2010 01:01:08 Steve Bennett wrote:
On 13/04/2010, at 11:09 AM, Rob Landley wrote:
> On Tuesday 13 April 2010 10:08:56 Kim B. Heino wrote:
>> BusyBox 1.16.1 on a small armv4tl system:
>>
>> $ time hwclock -w
>> real 0m 24.34s
>> user 0m 0.00s
>> sys 0m 0.00s
>>
>> $ time hwclock -w
>> real 0m 24.07s
>> user 0m 0.01s
>> sys 0m 0.00s
>>
>> $ time hwclock -w
>> real 0m 24.20s
>> user 0m 0.00s
>> sys 0m 0.00s
>>
>> rem_usec seems to be about 996600 after every iteration. Changing
>> sync
>> resolution from 1ms to 5ms helps, but there has to be better
>> solution.
>> Denys?
>
> I can confirm this on my armv4tl system image:
>
> wget
>
> http://impactlinux/com/fwl/downloads/binaries/system-image-armv4tl.tar.bz
>2 tar xvjf system-image-armv4tl.tar.bz2
> cd system-image-armv4tl
> ./run-emulator.sh
>
> wait through the boot messages...
>
> (armv4tl) /home # time hwclock -w
> real 0m 24.98s
> user 0m 0.01s
> sys 0m 0.01s
>
> This assumes you have qemu 0.12.x installed.
>
> Rob
>
> P.S: As expected, application emulation is useless here:
>
> $ qemu-arm ./hwclock
> Unsupported ioctl: cmd=0xffffffff80247009
> hwclock: RTC_RD_TIME: Function not implemented
Interesting.
BusyBox v1.17.0.git
armv5teb
~ # strace hwclock -w
... blah blah ...
open("/etc/adjtime", O_RDONLY) = -1 ENOENT (No such file or
directory) open("/dev/rtc", O_WRONLY) = -1 ENOENT (No such
file or directory) open("/dev/rtc0", O_WRONLY) = 3
gettimeofday({1271224598, 269609}, NULL) = 0
open("/etc/config/TZ", O_RDONLY) = 4
read(4, "EST-10\n", 68) = 7
read(4, "", 61) = 0
close(4) = 0
... lots of these ...
open("/etc/config/TZ", O_RDONLY) = 4
read(4, "EST-10\n", 68) = 7
read(4, "", 61) = 0
close(4) = 0
gettimeofday({1271224622, 14271}, NULL) = 0
nanosleep({0, 984729000}, NULL) = 0
gettimeofday({1271224623, 8166}, NULL) = 0
That's a largeish looking nanosleep.
At a guess, that would be this util-linx/hwclock.c snippet:
/* Try to sync up by sleeping */
rem_usec = 1000000 - tv.tv_usec;
if (rem_usec < 1024) {
goto small_rem; /* already close, don't sleep */
}
/* Need to sleep.
* Note that small adj on slow processors can make us
* to always overshoot tv.tv_usec < 1024 check on next
* iteration. That's why adj is increased on each iteration.
* This also allows it to be reused as a loop limiter.
*/
usleep(rem_usec - adj);
I'm guessing the tv.tv_usec is larger than 1000000 and thus it wraps?
When CELF is over, I should look at what gettimeofday() is returning to
fill in
the tv field. Right now, I'm at a conference and thus a bit
overscheduled...
Rob
If the condition (rem_usec < 1024) is never met, which seems to be the
case
on my system
with timer tick of 10ms, it will take (1024-200)/32=25.75 seconds to
execute
the hwclock
command.
I fixed syncing code so that it widens sync window very fast.
But then I disabled it anyway, it's too big and in my testing,
RTC isn't setting time with ~0.5sec precision anyway (!!!).
Fixed in git, will be in 1.16.2
--
vda
Couple remarks:
1. Why would we care to synchronize time in from_sys_clock()
and not to do it in to_sys_clock()?
2. Linux kernel will attempt to update RTC at 500ms mark and
not at a second mark. Do they known something better?
--
Piotr
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