Messages in this thread | | | Date | Wed, 6 May 2009 15:51:15 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH] v4 RCU: the bloatwatch edition |
| |
On Wed, May 06, 2009 at 11:22:54PM +0100, David Howells wrote: > Andrew Morton <akpm@linux-foundation.org> wrote: > > > More like "concerns". It's unobvious to me that the modest .text > > savings justify the costs of an additional RCU implementation. Where > > those costs include > > It may be more than just modest .text savings. Being optimised to be as > simple as possible, and to only support one CPU, it may be quicker too. I'm > not sure how best to benchmark it though.
The read side is unchanged, but the update side is another story, given that synchronize_rcu()'s latency decreases from multiple milliseconds to the sub-microsecond range:
void synchronize_rcu(void) { unsigned long flags;
local_irq_save(flags); rcu_ctrlblk.completed++; local_irq_restore(flags); }
So boot speed is one possible metric, depending on how many synchronize_rcu() invocations are in your arch's boot path. It appears that x86 has a fair number. ;-)
Thanx, Paul
| |