Re: [RFC&PATCH] Alternative RCU implementation

[Paul E. McKenney]

On Mon, Aug 30, 2004 at 01:13:41PM -0400, Jim Houston wrote:
> I know that I'm questioning one of your design goals for RCU by adding
> overhead to the read-side.  I have read everything I could find on RCU.
> My belief is that the cost of the xchg() instruction is small 
> compared to the cache benifit of freeing memory more quickly.
> I think it's more interesting to look at the impact of the xchg() at the
> level of an entire system call.  Adding 30 nanoseconds to a open/close
> path that tasks 3 microseconds seems reasonable.  It is hard to measure
> the benefit of reusing the a dcache entry more quickly.

Hello, Jim,

The other thing to keep in mind is that reducing the grace-period
duration increases the per-access overhead, since each grace period
incurs a cost.  So there is a balance that needs to be struck between
overflowing memory with a too-long grace period and incurring too
much overhead with a too-short grace period.

How does the rest of the kernel work with all interrupts to
a particular CPU shut off?  For example, how do you timeslice?

						Thanx, Paul

PS.  My concerns with some aspects of your design aside, your
     getting a significant change to the RCU infrastructure to
     work reasonably well is quite impressive!
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