Hi Eric, On Mon, Jan 22, 2018 at 10:16:06AM -0800, Eric Dumazet wrote: > On Mon, 2018-01-22 at 09:28 -0800, Ben Greear wrote: > > My test case is to have 6 processes each create 5000 TCP IPv4 connections > > to each other > > on a system with 16GB RAM and send slow-speed data. This works fine on a > > 4.7 kernel, but > > will not work at all on a 4.13. The 4.13 first complains about running out > > of tcp memory, > > but even after forcing those values higher, the max connections we can get > > is around 15k. > > > > Both kernels have my out-of-tree patches applied, so it is possible it is > > my fault > > at this point. > > > > Any suggestions as to what this might be caused by, or if it is fixed in > > more recent kernels? > > > > I will start bisecting in the meantime... > > > > Hi Ben > > Unfortunately I have no idea. > > Are you using loopback flows, or have I misunderstood you ? > > How loopback connections can be slow-speed ?
A few quick points : I have not noticed this on 4.9, which we use with pretty satisfying performance (typically around 100k conn/s). However during some recent tests I did around the meltdown fixes on 4.15, I noticed a high connect() or bind() cost to find a local port when running on the loopback, that I didn't have the time to compare to older kernels. However, strace clearly showed that bind() (or connect() if bind was not used) could take as much as 2-3 ms as source ports were filling up. To be clear, it was just a quick observation and anything could be wrong there, including my tests. I'm just saying this in case it matches anything Ben has observed. I can try to get more info if that helps, but it could be a different case. Cheers, Willy
