Re: CVS commit: src/share/man/man4

[maya%NetBSD.org@localhost]

On Fri, Apr 10, 2020 at 11:19:02AM +0900, SAITOH Masanobu wrote:
> On 2020/04/10 2:42, David Young wrote:
> > On Thu, Apr 09, 2020 at 03:25:32PM +0900, SAITOH Masanobu wrote:
> > > On 2020/04/09 11:08, David Young wrote:
> > > > On Wed, Apr 08, 2020 at 11:01:52PM +0000, Jaromir Dolecek wrote:
> > > > > 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*.
> > > 
> > > m_defrag() was added to -current in September 2018, and 9.0,
> > > 8.1, post 7.2 have this code.
> > 
> > Thank you, that's just the change I was thinking of.
> 
> You're welcome.
> Some drivers still have no m_defrag() code, so we should add it
> to them().


I had to stop using m_defrag because implementation details broke
bwfm@pci. It can only handle a chain of length 1, and m_defrag gives
a minimum of 2.