On Wed, 2015-04-22 at 06:04 +0200, Steinar H. Gunderson wrote: > On Tue, Apr 21, 2015 at 08:35:21PM +1000, jb wrote: > > As I understand it (I thought) SO_SNDBUF and SO_RCVBUF are socket buffers > > for the application layer, they do not change the TCP window size either > > send or receive. > > I haven't gone into the code and checked, but from practical experience I > think you're wrong. I've certainly seen positive effects (and verified with > tcpdump) from reducing SO_SNDBUF on a server that should have no problems at > all sending data really fast to the kernel.
Well, using SO_SNDBUF disables TCP autotuning. Doing so : Pros: autotuning is known to enable TCP cubic to grow cwnd to bloat levels. With small enough SO_SNDBUF, you limit this cwnd increase. Cons: Long rtt sessions might not have enough packets to utilize bandwidth. > > Then again, this kind of manual tuning trickery got obsolete for me the > moment sch_fq became available. Note that I suppose the SO_MAX_PACING rate is really helping you. Without it, TCP cubic is still allowed to 'fill the pipes' until packet losses. _______________________________________________ Bloat mailing list Bloat@lists.bufferbloat.net https://lists.bufferbloat.net/listinfo/bloat
