Re: RCU question

[Dipankar Sarma <dipankar@in.ibm.com>]

On Fri, Dec 10, 2004 at 11:42:55AM -0800, George Anzinger wrote:
> Dipankar Sarma wrote:
> >And yes, RCU processing in softirq context can re-raise the softirq.
> >AFAICS, it is perfectly normal.
> 
> My assumption was that, this being the idle task, RCU would be more than 
> happy to finish all its pending tasks.

We try to avoid really long running softirqs (RCU tasklet in this case)
for better scheduling latency. A long running rcu tasklet during
an idle cpu may delay running of an RT process that becomes runnable
during the rcu tasklet.

> 
> It may be necessary for me to rethink the conditions required to go into 
> the VST state.  I had assumed that it required NO softirq pending as a pre 
> condition. From this point on we would have the interrupt system off until 
> the hardware sleep instruction (hlt in the x86 case).

Unfortunately, we aren't there yet. But it is in my TODO list for a 
generic nohz system.

Thanks
Dipankar