Messages in this thread | | | Date | Fri, 22 Aug 2008 08:28:00 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH 2/2] smp_call_function: use rwlocks on queues rather than rcu |
| |
* Jeremy Fitzhardinge <jeremy@goop.org> wrote:
> RCU can only control the lifetime of allocated memory blocks, which > forces all the call structures to be allocated. This is expensive > compared to allocating them on the stack, which is the common case for > synchronous calls. > > This patch takes a different approach. Rather than using RCU, the > queues are managed under rwlocks. Adding or removing from the queue > requires holding the lock for writing, but multiple CPUs can walk the > queues to process function calls under read locks. In the common > case, where the structures are stack allocated, the calling CPU need > only wait for its call to be done, take the lock for writing and > remove the call structure. > > Lock contention - particularly write vs read - is reduced by using > multiple queues.
hm, is there any authorative data on what is cheaper on a big box, a full-blown MESI cache miss that occurs for every reader in this new fastpath, or a local SLAB/SLUB allocation+free that occurs with the current RCU approach?
Ingo
| |