Re: [uml-devel] [PATCH v6] um: Add a high resolution timer subsystem

[Thomas Meyer <thomas@m3y3r.de>]

Am 11.05.2015 7:31 nachm. schrieb Anton Ivanov <anton.ivanov@kot-begemot.co.uk>:
>
> On 11/05/15 18:20, Anton Ivanov wrote: 
> > On 11/05/15 18:00, Thomas Meyer wrote: 
> >> Hi, 
> >> 
> >> maybe there is a bug in how the timers are created for all user space processes. 
> >> In the latest patch I use os__timer_remain for the initial interval. 
> >> The idea was to launch all timers at the same time. But I now think this can never work using relative times, especially when os__timer_remain returns 0, then the new timer is never launched. 
> > That is not a bad idea, just requires a more complex check in setting up 
> > interval so it is reset to default when a zero value or value > HZ is 
> > passed. 
> > 
> > 
> >> That may explain the hangs you see. 
> >>    You could try to replace os__timer_remain with the current HZ value in nanoseconds. 
> > I am going to adjust time.c instead as above. 
>
> Both approaches fail - the check (that is expected actually, I did not 
> think properly here - it does not cover the stub in kernel/skas) and the 
> setting of data to the correct initial values. 
>
> Also, if it was just not starting timers it would have been possible to 
> beat the process with USR2 on the head until its morale improves. Well, 
> "while true; do kill -USR2 PID ; done" does not change the behavior, it 
> still hangs and is still possible to terminate the errant process by 
> sending SIGSEGV to the UML thread which is shown as 100% CPU and in R state. 

Yes, sending USR2 should do the same. Correct.

>
> Problem is somewhere else. I am surprised it worked correctly in the 
> original one as there for 100% flat CPU usage it should have converged 
> to a behavior which is similar to what we have now. 

Mhh. Strange. Any hints how I can reproduce this?

I need to see the same behaviour, i.e. the hang on my machine to begin to understand what is going on here.

Thanks for testing Anton.


>
> A. 
>
> > 
> > A. 
> > 
> >> Kind regards 
> >> Thomad 
> >> 
> >> A 
> > [snip] 
> > 
> > A. 
> > 
> > ------------------------------------------------------------------------------ 
> > One dashboard for servers and applications across Physical-Virtual-Cloud 
> > Widest out-of-the-box monitoring support with 50+ applications 
> > Performance metrics, stats and reports that give you Actionable Insights 
> > Deep dive visibility with transaction tracing using APM Insight. 
> > http://ad.doubleclick.net/ddm/clk/290420510;117567292;y 
> > _______________________________________________ 
> > User-mode-linux-devel mailing list 
> > User-mode-linux-devel@lists.sourceforge.net 
> > https://lists.sourceforge.net/lists/listinfo/user-mode-linux-devel 
> > 
>
>
> ------------------------------------------------------------------------------ 
> One dashboard for servers and applications across Physical-Virtual-Cloud 
> Widest out-of-the-box monitoring support with 50+ applications 
> Performance metrics, stats and reports that give you Actionable Insights 
> Deep dive visibility with transaction tracing using APM Insight. 
> http://ad.doubleclick.net/ddm/clk/290420510;117567292;y 
> _______________________________________________ 
> User-mode-linux-devel mailing list 
> User-mode-linux-devel@lists.sourceforge.net 
> https://lists.sourceforge.net/lists/listinfo/user-mode-linux-devel 
------------------------------------------------------------------------------
One dashboard for servers and applications across Physical-Virtual-Cloud 
Widest out-of-the-box monitoring support with 50+ applications
Performance metrics, stats and reports that give you Actionable Insights
Deep dive visibility with transaction tracing using APM Insight.
http://ad.doubleclick.net/ddm/clk/290420510;117567292;y
_______________________________________________
User-mode-linux-devel mailing list
User-mode-linux-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/user-mode-linux-devel