Re: [PATCH] clean up FIXME in do_timer_interrupt

George Anzinger
2005-03-08T23:32:06Z

Lee Revell wrote:
> On Fri, 2005-03-04 at 12:58 -0800, George Anzinger wrote:
>
>>Lee Revell wrote:
>>
>>>On Fri, 2005-03-04 at 02:28 -0800, George Anzinger wrote:
>>>The thing that brought this code to my attention is that with PREEMPT_RT
>>>this happens to be the longest non-preemptible code path in the kernel.
>>>On my 1.3 Ghz machine set_rtc_mmss takes about 50 usecs, combined with
>>>the rest of timer irq we end up disabling preemption for about 90 usecs.
>>>Unfortunately I don't have the trace anymore.
>>>
>>>Anyway the upshot is if we hung this off a timer it looks like we would
>>>improve the worst case latency with PREEMPT_RT by almost 50%. Unless
>>>there is some reason it has to be done synchronously of course.
>>
>>Well, it does have to be done at the right WRT the second, but I suspect we can
>>hit that as well with a timer as it is hit now. Also, if we are _really_ off
>>the mark, this can be defered till the next second.
>>
>
>
> Do you have a patch?

Not at the moment, but I will work one up.
>
> Andrew merged my trivial patch to clean up the logic, but a real fix
> would be better.
>
> Lee
>

--
George Anzinger george@mvista.com
High-res-timers: http://sourceforge.net/projects/high-res-timers/