Re: [PATCH tip/core/rcu 13/23] rcu: Control grace-period durationfrom sysfs

[Peter Zijlstra]

On Thu, 2012-09-06 at 10:53 -0700, Paul E. McKenney wrote:

> >  - how do I know if my workload wants a longer or shorter forced qs
> >    period?
> 
> Almost everyone can do just fine with the defaults.  If you have more
> than about 1,000 CPUs, you might need a longer period. 

Because the cost of starting a grace period is on the same order (or
larger) in cost as this period?

>  Some embedded
> systems might need a shorter period -- the only specific example I know
> of is network diagnostic equipment running wireshark, which starts up
> slowly due to grace-period length.

But but but 3 jiffies.. however is that too long?

> > Also, whatever made you want to provide this 'feature' in the first
> > place?
> 
> Complaints from the two groups called out above.

Does this really warrant a boot time knob for which even you cannot
quite explain what values to use when?


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