Re: RCU latency regression in 2.6.16-rc1

[Lee Revell <rlrevell@joe-job.com>]

On Tue, 2006-01-24 at 10:23 +0100, Ingo Molnar wrote:
> * Paul E. McKenney <paulmck@us.ibm.com> wrote:
> 
> > > Have not tested yet but it appears that will reduce it substantially:
> > > 
> > > $ grep "dst_destroy (dst_rcu_free)" /proc/latency_trace | wc -l
> > > 3027
> > > 
> > > This implies the latency would be reduced to ~4ms, still not great but
> > > it will be overshadowed by rt_run_flush/rt_garbage_collect.
> > 
> > The other patch to try would be Dipankar Sarma's patch at:
> > 
> > 	http://marc.theaimsgroup.com/?l=linux-kernel&m=113657112726596&w=2
> > 
> > This patch was primarily designed to reduce memory overhead, but given 
> > that it tends to reduce batch size, it should also reduce latency.
> 
> if this solves Lee's problem, i think we should apply this as a fix, and 
> get it into v2.6.16. The patch looks straightforward and correct to me.
> 

Does not compile:

 CC      kernel/rcupdate.o
kernel/rcupdate.c:76: warning: 'struct rcu_state' declared inside parameter list
kernel/rcupdate.c:76: warning: its scope is only this definition or declaration, which is probably not what you want
kernel/rcupdate.c: In function 'call_rcu':
kernel/rcupdate.c:113: error: 'rcu_state' undeclared (first use in this function)
kernel/rcupdate.c:113: error: (Each undeclared identifier is reported only once
kernel/rcupdate.c:113: error: for each function it appears in.)
kernel/rcupdate.c: In function 'call_rcu_bh':
kernel/rcupdate.c:155: error: 'rcu_bh_state' undeclared (first use in this function)
make[1]: *** [kernel/rcupdate.o] Error 1
make: *** [kernel] Error 2

Lee