On 24/12/16 14:22, Steffan Karger wrote: > This patch is not done, but I would like to get some early feedback > because I'm not very familiar with this part of the code, nor with the > APIs involved. So I expect to have made some rooky mistakes. > > A while back, I experimented a bit with recvmmsg(), to see if using it > would yield some performance gain. Simple tests (I don't have a good > stress test setup handy) indicate that this improves throughput by a few > percent. I would expect more gain on the server side for P2MP servers > though, where multiple client can be spamming the server at once. > > What definitely still needs to be done: > * Improve error messages > * Improve documentation (doxygen, openvpn.8, Changes.rst) > * Figure out good default values > > So, please, let me know what you think of the code. And if you do have > a good setup for performance testing, I'd love to hear what this change > does for you.
Too bad I have changed employer ... as I have some vague memories doing some recvmmsg() send even sendmmsg() testing on kernel-rt, when these features were added there. I'll meet some of my ex-colleagues later this week and weekend (devconf.cz happens now) ... so I'll see if I can get some help retrieving some reasonable test scenarios. So to the patch ... First of all, not all kernels carry these system calls, I believe they were added in some of the 3.x kernels - but, IIRC, it has been backported to at least the RHEL6 2.6.32 kernels. My memory is scarce about the 2.6.18 kernel base on RHEL5, but I believe only recvmmsg() is supported there. But kernel support isn't enough. It needs to be supported in glibc as well, where recvmmsg() arrived in glibc-2.12 and sendmmsg() arrived in glibc-2.14. And if glibc support is missing ... there's needed to so some tweaks here, having a wrapper which does the proper syscall() with SYS_recvmmsg and/or SYS_sendmmsg as the syscall number reference. (see /usr/include/bits/syscall.h and man syscall(2) for more info) ... but step carefully with such wrappers - as we need to consider cross-platforms (not saying we should support this feature on all platforms). So all this considered, configure.ac will need to do some probing if recvmmsg() and sendmmsg() are supported. I know this patch covers recvmmsg() only. But I think you can gain even more performance if looking into sendmmsg() as well. I'll try to play a bit with this patch and see how things go on my side though. -- kind regards, David Sommerseth OpenVPN Technologies, Inc
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