On Wed, Nov 20, 2013 at 05:36:00PM -0500, Chris Burroughs wrote: > Using 1.4.24 without USE_LINUX_SPLICE=1 results in an error when setting > 'defaults option splice-auto', and maxpipes is reported as zero. This > makes sense. > > With USE_LINUX_SPLICE=1 I get maxpipes == maxconn/4 as the docs say. > However, "current pipes" is always listed as 0/0, even under load. Does > that mean that splice is not working (or not being used)? Is there a > way to confirm splice it is working besides that metric?
That means that no pipes were allocated because not needed. It does not mean it's not working because in order to detect that splice is not working, you need at least one pipe. Thus it would be more suspicious if you had "0/1" :-) Splice-auto attempts to switch to splicing only when it seems to make sense, which is when haproxy detects that buffers are read at once and flushed at once. So that only applies to large transfers. If you download a 1 MB object, it is very likely that the first few kB will be transferred normally and that splice would be used afterwards. You can force to use it for all responses whatever their size using "splice-response" if you want to see it in action. Note that with a number of network cards, it provides no gain and can even reduce the performance because of the limit imposed by the pipe size (64k - 16 pages or 16 segments depending on the driver). > This is centos6 so it's kernel 2.6.32 + crazy RedHat stuff > (2.6.32-358.23.2.el6.x86_64). It normally works on 2.6.32, even with RH stuff :-) On 2.6.32, splicing works very well with certain NIC drivers such as Myri10GE when you have LRO enabled on the NIC. For most other NICs not supporting LRO, it might be useless. With more recent kernels starting at 3.5 and onwards, GRO works much better than before with splicing, to the point that it can be worth enabling even with smaller objects and more NICs. I could easily achieve 40 Gbps of forwarded traffic in 3.8 with 2 dual-port ixgbe NICs and LRO or GRO enabled. Willy
