Re: [PATCH] hwclock: flush stdout in hwclock -c

[J William Piggott <elseifthen@gmx.com>]

On 04/21/2015 11:50 AM, Alexey Galakhov wrote:
> Am Tue, 21 Apr 2015 11:19:06 -0400
> schrieb J William Piggott <elseifthen@gmx.com>:
> 
>> I assume then, that you are only using columns one and two, because
>> columns 3 and 4 are invalid output.
> 
> IN the beginning I used column 3. By examining the source code I
> figured out that it is suitable for such kind of tests, at least
> if /etc/adjtime is empty.
> 
>> Your test could capture timestamps without hwclock's compare
>> function, yes?
> 
> Right now I reimplemented the whole (simplified) hwclock -c
> functionality in my own test. In fact, I recalculate column 3 on my own.
> 
> What I really want to see is a "correct" column 3. In my test I'm doing
> direct comparison.

So you are confirming my position that hwclock's compare function is
broken and that you are not using it for any useful purpose.


> Pseudocode:
> 
> while(1) {
>     do { // busy-wait
>         t1 = clock_gettime();
>         t2 = ioctl(RTC);
>     } while t2 does not change;
>     
>     drift = (t1 - t2) / total time;
> 
>     sleep(until t1 + 990ms);
> }
> 
> My test fails if a relative drift is more than expected with such a
> hardware. This is useful to quickly detect stupid bugs like wrong PLL
> configuration on new hardware ("time runs 10% faster" and so on). The
> reason why we do so is, nobody really cares about the system clock
> while installing the kernel and base system. Thus the problem is
> detected only when the complete user level is up and running, and
> nobody wants to touch the bootloader and the kernel at this time. So we
> created a bunch of "early warning tests" to detect non-obvious kernel
> and hardware issues.

Thank you for the detailed explanation Alexey. I can see how comparing
the System and Hardware clocks is useful for your situation and worthy
of a specialize test as you have written. In my opinion, comparing two
drifting clocks is not useful to end users, system administrators, or
distribution maintainers and I am hopeful that Karel will agree to its
removal from hwclock.

> 
> Regards,
> Alexey
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