On Mon, Nov 04, 2013 at 02:44:38PM -0800, Jarno Rajahalme wrote: > Add a FAQ categorry "Performance Problems". So far the only entry > addresses the issue with using a new kernel module with an older > (pre-megaflows) userspace. > > Signed-off-by: Jarno Rajahalme <[email protected]>
What if we just name the section "Performance"? I can see a demand for broad explanations of OVS performance, as well as descriptions of performance problems. > +Performance Problems > +-------------------- > + > +Q: I just upgraded and I see a performance drop. Why? > + > +A: Sometimes support for new protocol fields is added to OVS. If a > + new OVS kernel module is paired with an older (pre 1.11) OVS > + userspace, there may be a preformance drop. In particular, when > + the new fields concern existing and widely used protocols, old > + implementations may face a drop in performance. Since OVS release > + 1.11, which added kernel wildcarding, this should be less of an > + issue, as any new fields not understood by the userspace remain > + automatically wildcarded. > + > + For example, OVS release 2.1 added support for TCP flags matching. > + Pairing a new OVS kernel module with OVS userspace without kernel > + wildcarding, each TCP flags combination for each TCP connection > + appears as a separate flow miss for the OVS userspace, multiplying > + the required flow setups in most (TCP-heavy) workloads. > + > + Upgrading the OVS userspace components will resolve these > + performance issues. To me, this seems pretty difficult to understand. I understand it, because I know the underlying issues, but I am not sure that a casual reader would. Perhaps we could rephrase it by starting the answer out with an explanation that some kernel/userspace combinations do not perform as well as others, that it is best to pair the same versions of each, and then list very clearly the combinations that perform worst. Also, it is probably worth mentioning not just OVS versions but upstream kernel versions (since a lot of users would prefer to avoid compiling a separate module if they can). An actual explanation of the technical reasons for the performance differences is nice, but it's probably not what most users really want when they read this FAQ. _______________________________________________ dev mailing list [email protected] http://openvswitch.org/mailman/listinfo/dev
