[lkml]   [2018]   [Jan]   [28]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCH] kdb: use ktime_get_seconds() instead of ktime_get_ts()
On 27 January 2018 at 00:01, Arnd Bergmann <> wrote:
> On Fri, Jan 26, 2018 at 3:20 PM, Baolin Wang <> wrote:
>> On 26 January 2018 at 22:00, Daniel Thompson <> wrote:
>>> On Fri, Jan 26, 2018 at 10:21:58AM +0100, Arnd Bergmann wrote:
>>>> On Fri, Jan 26, 2018 at 4:03 AM, Baolin Wang <> wrote:
>>>> Using ktime_get_seconds() avoids locking problems, but I wonder what
>>>> would happen if we trigger the 'WARN_ON(timekeeping_suspended)'
>>>> from kdb. Is that a problem? If it is, we have to use ktime_get_mono_fast_ns()
>>>> and div_u64() instead.
>>> Normally a WARN_ON() doesn't triggered a kgdb_breakpoint() so (apart
>>> from bugs) we can start executing the warning. Unfortunately
>>> kdb_trap_printk isn't set when we call ktime_get_seconds() so printing
>>> the warning isn't safe.
>>> If we had no choice of time function we could work around by
>>> enabling printk() trapping for the call but since ktime_get_mono_fast_ns()
>>> already exists its probably best just to use that.
>> If timekeeping_suspended is set, which means the system had been in
>> suspend state. So now we still need debugger the system? But cores
>> were already powered down.
> I'm not using kdb myself, but I would assume that trapping into the debugger
> during a suspend/resume bug is a very important scenario.
>> The ktime_get_mono_fast_ns() will access the the clocksource driver,
>> if the timekeeping is suspended following system suspend and the
>> clocksource is not SUSPEND_NONSTOP, we may meet some unexpected issue
>> to access the timer's register without clock. So I am not sure if
>> ktime_get_mono_fast_ns() can work well for this case.
> I misread the code the same way before, but as Thomas Gleixner
> pointed out, ktime_get_mono_fast_ns() will not call the clocksource
> driver when timekeeping is suspended. See halt_fast_timekeeper().

Ah, I missed halt_fast_timekeeper() too, thanks for pointing it out.
Now I think ktime_get_mono_fast_ns() can work for this case.

Jason, could you drop the previous patch? I will respin v2 to use
ktime_get_mono_fast_ns() as Arnd suggested. Thanks.

Best Regards

 \ /
  Last update: 2018-01-29 02:50    [W:0.152 / U:5.020 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site