linux-kernel - Re: changing timeslice in linux

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Message-ID: <CALKntY0WgYBPfJ0aG=oqLctJf-EOmAdKBWqnA64x8p9tdVQDXA@mail.gmail.com>
Date:	Tue, 28 Aug 2012 13:16:47 -0700
From:	Xin Tong <xerox.time.tech@...il.com>
To:	Namhyung Kim <namhyung@...nel.org>
Cc:	Mike Galbraith <efault@....de>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: changing timeslice in linux

another question is that when i try to launch many (24) RT processes.
some of them do not seem to get scheduled. i query their scheduling
properties. they all have SCHED_RR with priority 99, but some of them
simply are not taking any CPU.

Xin


On Tue, Aug 28, 2012 at 1:15 PM, Xin Tong <xerox.time.tech@...il.com> wrote:
> i changed the TIMESLICE defined in the sched.c
>
>   109 /*
>   110  * These are the 'tuning knobs' of the scheduler:
>   111  *
>   112  * default timeslice is 100 msecs (used only for SCHED_RR tasks).
>   113  * Timeslices get refilled after they expire.
>   114  */
>   115 #define DEF_TIMESLICE           (20 * HZ / 1000)
>
>
> I compiled and installed the modified kernel, but when i looked at the
> , i get a different number
>
> root@elm:~# cat /proc/sys/kernel/sched_rt_period_us
> 1000000
>
>
> Xin
>
> On Mon, Aug 20, 2012 at 5:16 PM, Namhyung Kim <namhyung@...nel.org> wrote:
>> On Mon, 20 Aug 2012 07:51:52 -0700, Xin Tong wrote:
>>> On Sun, Aug 19, 2012 at 10:54 PM, Mike Galbraith <efault@....de> wrote:
>>>> On Sun, 2012-08-19 at 11:58 -0700, Xin Tong wrote:
>>>>> I have 2 questions about linux 2.6 x86_64 scheduler.
>>>>>
>>>>> 1. is the default scheduling algorithm SCHED_NORMAL in linux ?
>>>>
>>>> Yes.
>>> Is there any document describing what the sched_normal is ? it is more
>>> difficult than SCHED_RR to infer its meaning just based on its name ?
>>>>
>>>>> 2. how do i change the time slice in linux source code ?
>>>>
>>>> You shouldn't need to.  You can tune "slice" by adjusting
>>>> sched_latency_ns and sched_min_granularity_ns, but note that "slice" is
>>>> not a fixed quantum.  Also note that CFS preemption decisions are based
>>>> upon instantaneous state.  A task may have received a full (variable)
>>>> "slice" of CPU time, but preemption will be triggered only if a more
>>>> deserving task is available, so a "slice" is not the "max uninterrupted
>>>> CPU time" that you may expect it to be.. but it is somewhat similar.
>>>>
>>>> -Mike
>>>>
>>> This can be done without recompiling and reinstalling the kernel ?
>>> maybe one simply needs to write to a device file under /dev ?
>>
>> You can find those files under /proc/sys/kernel/.
>>
>> Thanks,
>> Namhyung
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