lkml.org 
[lkml]   [2013]   [Apr]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 5/5] sched: limit sched_slice if it is more than sysctl_sched_latency
Hello, Preeti.

On Mon, Apr 01, 2013 at 12:15:50PM +0530, Preeti U Murthy wrote:
> Hi Joonsoo,
>
> On 04/01/2013 10:39 AM, Joonsoo Kim wrote:
> > Hello Preeti.
> > So we should limit this possible weird situation.
> >>>
> >>> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> >>>
> >>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> >>> index e232421..6ceffbc 100644
> >>> --- a/kernel/sched/fair.c
> >>> +++ b/kernel/sched/fair.c
> >>> @@ -645,6 +645,9 @@ static u64 sched_slice(struct cfs_rq *cfs_rq, struct sched_entity *se)
> >>> }
> >>> slice = calc_delta_mine(slice, se->load.weight, load);
> >>>
> >>> + if (unlikely(slice > sysctl_sched_latency))
> >>> + slice = sysctl_sched_latency;
> >>
> >> Then in this case the highest priority thread would get
> >> 20ms(sysctl_sched_latency), and the rest would get
> >> sysctl_sched_min_granularity * 10 * (1024/97977) which would be 0.4ms.
> >> Then all tasks would get scheduled ateast once within 20ms + (0.4*9) ms
> >> = 23.7ms, while your scheduling latency period was extended to 40ms,just
> >> so that each of these tasks don't have their sched_slices shrunk due to
> >> large number of tasks.
> >
> > I don't know I understand your question correctly.
> > I will do my best to answer your comment. :)
> >
> > With this patch, I just limit maximum slice at one time. Scheduling is
> > controlled through the vruntime. So, in this case, the task with nice -20
> > will be scheduled twice.
> >
> > 20 + (0.4 * 9) + 20 = 43.9 ms
> >
> > And after 43.9 ms, this process is repeated.
> >
> > So I can tell you that scheduling period is preserved as before.
> >
> > If we give a long period to a task at one go, it can cause
> > a latency problem. So IMHO, limiting this is meaningful.
>
> Thank you very much for the explanation. Just one question. What is the
> reason behind you choosing sysctl_sched_latency as the upper bound here?

sysctl_sched_latency is a sched_slice when there is one task.
So, I think that this is proper as upper bound.

Thanks.

> Regards
> Preeti U Murthy
>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at http://www.tux.org/lkml/


\
 
 \ /
  Last update: 2013-04-02 04:21    [W:0.186 / U:0.032 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site