Re: kern/55567: tcp-send slows down to slow single byte transfers (analysis and fix)

[Frank Kardel <kardel%netbsd.org@localhost>]

The following reply was made to PR kern/55567; it has been noted by GNATS.

From: Frank Kardel <kardel%netbsd.org@localhost>
To: Jason Thorpe <thorpej%me.com@localhost>
Cc: kern-bug-people%netbsd.org@localhost, gnats-admin%netbsd.org@localhost,
 netbsd-bugs%netbsd.org@localhost, gnats-bugs%netbsd.org@localhost
Subject: Re: kern/55567: tcp-send slows down to slow single byte transfers
 (analysis and fix)
Date: Wed, 2 Sep 2020 17:00:35 +0200

 Thanks for double checking!
 
 Frank
 
 
 On 09/02/20 16:58, Jason Thorpe wrote:
 >> On Sep 2, 2020, at 1:05 AM, Frank Kardel <kardel%netbsd.org@localhost> wrote:
 >>
 >> The path taken that leads to SND.WL2 being starved out is the pure ACK
 >> section
 >> which adjusts the send buffer, updates SND.UNA, SND.FACK, SND.HIGH,
 >> frees mbuf
 >> , send more data if available and returns.
 >> SND.WL2 is never touched here an so a longer sequence can leave SND.WL2
 >> far enough
 >> behind for the stuck zero window size to occur.
 >>
 >> Proposed fix:
 > Frank --
 >
 > This analysis looks right to me, and your proposed fix looks correct.  It looks like FreeBSD also has an equivalent assignment to SND.WL2 in the same spot for quite a while now, so I would say the change has had some solid bake time already.  Ship it!
 >
 > -- thorpej
 >