Messages in this thread |  | | Date | Wed, 13 Nov 2013 17:21:53 +0100 (CET) | From | Thomas Gleixner <> | Subject | Re: nohz problem with idle time on old hardware |
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On Wed, 13 Nov 2013, Thomas Gleixner wrote:
> On Wed, 13 Nov 2013, Steven Rostedt wrote: > > > On Wed, 13 Nov 2013 10:31:34 -0500 > > Steven Rostedt <rostedt@goodmis.org> wrote: > > > > > The trace does indeed show that a tick is happening, as the config has > > > HZ=250 (4ms) and we see a tick happen every 4ms. But for some reason, > > > we don't update the the idle time correctly when nohz is enabled. > > > > > > When I say nohz is enabled, I mean that we don't have nohz=off in the > > > command line. There seems to be some difference between having nohz=off > > > and having nohz disabled at runtime. > > > > > > Looking at the differences between nohz=off from the command line, and > > disabled at run time seems to be the variable "tick_nohz_enabled". I > > don't see where it gets set to zero except for nohz=off. > > Right. It's telling you if NOHZ is enabled. It's not telling you that > NOHZ is active.
And its even worse:
tick_nohz_idle_enter()
/* * set ts->inidle unconditionally. even if the system did not * switch to nohz mode the cpu frequency governers rely on the * update of the idle time accounting in tick_nohz_start_idle(). */ ts->inidle = 1;
So there is code relying on that accounting stuff even if nohz is not active.
Frozen shark time ....
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