Re: [patch 1/2] rcu batch tuning

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

On Thu, Jan 26, 2006 at 11:33:17AM -0800, Paul E. McKenney wrote:
> On Fri, Jan 27, 2006 at 12:11:27AM +0530, Dipankar Sarma wrote:
> > 
> > This patch adds new tunables for RCU queue and finished batches.
> > There are two types of controls - number of completed RCU updates
> > invoked in a batch (blimit) and monitoring for high rate of
> > incoming RCUs on a cpu (qhimark, qlowmark). By default,
> > the per-cpu batch limit is set to a small value. If
> > the input RCU rate exceeds the high watermark, we do two things -
> > force quiescent state on all cpus and set the batch limit
> > of the CPU to INTMAX. Setting batch limit to INTMAX forces all
> > finished RCUs to be processed in one shot. If we have more than
> > INTMAX RCUs queued up, then we have bigger problems anyway.
> > Once the incoming queued RCUs fall below the low watermark, the batch limit
> > is set to the default.
> 
> Looks good to me!  We might have to have more sophisticated adjustment
> of blimit, but starting simple is definitely the right way to go.

Yes. Once I am set up to do latency measurements, I will look at
the possible need for more sophisticated adjustment of blimit.

Thanks
Dipankar