Re: [uml-devel] [PATCH v3] um: Switch clocksource to hrtimers

[Thomas Meyer <thomas@m3y3r.de>]

Am Samstag, den 31.10.2015, 16:30 +0100 schrieb Richard Weinberger:
> Am 31.10.2015 um 16:24 schrieb Thomas Meyer:
> > Am Samstag, den 31.10.2015, 16:21 +0100 schrieb Richard Weinberger:
> > > Am 31.10.2015 um 16:16 schrieb Thomas Meyer:
> > > > mhh. strange. I didn't see this behaviour on my machine, but my
> > > > machine
> > > > is a rare single core system so, likely a race condition while
> > > > relaying
> > > > the timer interrupt to the userspace process.
> > > 
> > > Here I can trigger it by starting UML, logging in and waiting
> > > ~5min.
> > > Then i try to run "top" --> top hangs forever.
> > > 
> > > > But I'm out of ideas how this could happen!
> > > 
> > > Maybe some stupid timeslice over/underflow.
> > > 
> > > > what happens when you send the hanging process a SIGVTALRM
> > > > signal?
> > > > does
> > > > it proceed correctly?
> > > 
> > > You mean sending SIGVTALRM to the UML host process?
> > 
> > No, to the hanging userspace process, maybe the uml host process
> > did
> > receive a timer interrupt, but failed to relay this signal to the
> > correct userspace process.
> 
> Well, this is not what top expects and dies.
>         signal 26 (VTALRM) was caught by top, please
>         see http://www.debian.org/Bugs/Reporting
> 

So you did send a VTALARM in the UML system to the top process?
When yes then this was a misunderstanding! I wanted you to send a
SIGVTALRM on the uml host system to the hanging pid. does this resolve
the hang?


> The problem is within UML's scheduler it does not wake top
> after the nanosleep() expires.
> Maybe the new clock is too imprecise, dunno.
> 
> Thanks,
> //richard
> 
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