On Wed, Apr 08, 2020 at 11:01:52PM +0000, Jaromir Dolecek wrote: > Module Name: src > Committed By: jdolecek > Date: Wed Apr 8 23:01:52 UTC 2020 > > Modified Files: > src/share/man/man4: wm.4 > > Log Message: > add a warning in checksum offload that hardware TCP segmentation might be > slow > > on I219 I observe about 35% transmit performance drop when tso4 enabled
This sounds familiar. There was a bug affecting TCP segmentation offload (I think) that we found at CoyotePoint. ISTR bus_dmamap_load_mbuf(9) failed with EFBIG because under some circumstances the number of segments in the DMA map was too small for the mbuf chain. The driver would drop the whole mbuf chain on the floor. This showed up as terrible performance under some circumstances---possibly when the TCP window grew long? The solution was to increase the number of DMA segments, *I think*. I don't think CoyotePoint ever fed its change back to NetBSD, unfortunately. On the other hand, some other NetBSDer may have independently fixed the bug. Do any stats increase (vmstat -e, ifconfig -v wm0) when the poor performance occurs? You may have to enable WM_DEBUG or something to see all of the relevant stats. Dave -- David Young dyo...@pobox.com Urbana, IL (217) 721-9981