lkml.org 
[lkml]   [2018]   [Nov]   [20]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 18/25] vtime: Track nice-ness on top of context switch
On Wed, Nov 14, 2018 at 03:46:02AM +0100, Frederic Weisbecker wrote:
> We need to read the nice value of the task running on any CPU, possibly
> remotely, in order to correctly support kcpustat on nohz_full.
> Unfortunately we can't just read task_nice(tsk) when tsk runs on another
> CPU because its nice value may be concurrently changed. There could be a
> risk that a recently modified nice value is thought to apply for a longer
> while than is supposed to.
>
> For example if a task runs at T0 with nice = -10, then its nice value
> is changed at T0 + 1 second with nice = 10, a reader at T0 + 1 second
> could think that the task had this "nice == 10" value since the beginning
> (T0) and spuriously account 1 second nice time on kcpustat instead of 1
> second user time.
>
> So we need to track the nice value changes under vtime seqcount. Start
> with context switches and account the vtime nice-ness on top of it.

Huh, what!? That doesn't make any sense..

\
 
 \ /
  Last update: 2018-11-20 15:10    [W:0.178 / U:0.336 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site