On Wed, Jan 16, 2013 at 01:59:21PM -0800, Ben Pfaff wrote: > On Tue, Jan 15, 2013 at 01:20:57PM +0900, Simon Horman wrote: > > Optimise OpenFlow flow expiry by placing expirable flows on a list. > > This optimises scanning of flows for expiry in two ways: > > > > * Empirically list traversal appears faster than the code it replaces. > > > > With 1,000,000 flows present an otherwise idle system I observed CPU > > utilisation of around 20% with the existing code but around 10% with > > this new code. > > > > * Flows that will never expire are not traversed. > > > > This addresses a case seen in the field. > > This version looks better. I still have a few comments, but before > that, may I ask a little bit about the situation in which the > performance improvement was observed? In this situation, about how > many of the 1,000,000 flows were actually expirable, that is, had > either a hard timeout or an idle timeout? That is, is the performance > improvement due more to the first or the second bullet you list above? > If none of the flows were expirable, then I guess it was the second; > if all of them were, then I guess it was the first; and otherwise it > is something in between. > > Basically I'm wondering if we should do something to make flow table > traversal faster, independent of expiration.
Hi Ben, the primary aim of this patch was to address a performance issue that was noticed when inserting 100,000 flows none of which were expirable. I have been told this is representative of an expected use-case. During my testing I used 1,000,000 flows instead of 100,000 in order to make the CPU utilisation more pronounced and easier to observe. In the course of my testing I tested 1,000,000 flows none of which were expirable and in that case CPU utilisation was dramatically reduced to approximately 0. This seems to be a good outcome for the use-case originally reported. In the course of testing I also tested 1,000,000 flows all of which were expirable. This was primarily to see if there were any regressions. In the course of this test I noticed that there seemed to be some reduction in CPU utilisation. However this was just a side effect and not an aim of my work. I should have placed it as the second bullet in my commit message and noted that it was a side effect. _______________________________________________ dev mailing list dev@openvswitch.org http://openvswitch.org/mailman/listinfo/dev
