[haiku-gsoc] Re: some questions about haiku kernel
- From: Yongcong Du <ycdu.vmcore@xxxxxxxxx>
- To: haiku-gsoc@xxxxxxxxxxxxx
- Date: Sat, 12 May 2012 21:17:52 +0800
Hi Axel,
On Sat, May 12, 2012 at 12:21 AM, Axel Dörfler <axeld@xxxxxxxxxxxxxxxx>wrote:
>
> On 11.05.2012 15:35, Yongcong Du wrote:
>
>> > I assume you mean if you remove the timer in case of the idle thread
>> > only?
>> all thread have the same behavior -- the oldThread and nextThread are
>> the same thread. But the phenomenon is obvious when the thread is the
>> idle thread. And I found that there is no such phenomenon if I
>> commented out the quantumTimer related code
>>
>
> The reason is simply scheduling: preemption is just one case of
> scheduling, but if you have longer running threads, they could run more or
> less forever without that timer, draining other long running threads (in
> this case with the same or a lower thread priority).
>
> The quantum is used to disrupt the thread, and look if another one should
> run next. You could disable the timer for the idle thread, as that one will
> always be preempted in order to save energy, but you cannot get rid of the
> timer completely.
Thanks very much. With your help, now I got the quantumTimer point. I can't
imagine haiku scheduler code is so tight(compared with linux thousands of
LOCs :D) and works well so far.
>
> After digging into the source code for one fully day, I still can't
>> understand what's reschedule_even used for
>>
>
> That's why you can always ask on this list ;-)
> If I didn't manage to write something understandable, please just ask
> again.
>
> HTH,
>
Appreciate your kind help,
Yongcong
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