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RE: X11 forwarding extremely slow (unusable) after Cygwin upgrade on Dec 23rd


I don't know if this will help at all since there is a big time gap and it
looks like a lot of changes between these, but I tried the cygwin1 dlls from
the snapshots at and found that the
2019-08-19 snapshot works fine, the next one dated 2019-11-03 introduces the

Someone told me offline that there were about half a dozen released versions
between 3.0.7-1 and 3.1.0-1, but those are not available to pull from any of
the mirrors that I tried. Anyone know if any of those intermediate versions
of cygwin1.dll may be available somewhere from which I can grab them to try
to narrow this down further?


> -----Original Message-----
> From: <>
> Sent: Wednesday, January 1, 2020 12:41 AM
> The problem is with cygwin 3.1.0-1, released on Dec 16th, or thereabouts.
> I decided to track it down by re-installing the earlier working release
> the Cygwin time machine at, and then
> incrementally upgrading it until the problem showed up. It turns out that
> was introduced in the Dec 16th release, which made just one change -
> upgraded cygwin from 3.0.7-1 to 3.1.0-1. With the Dec 15th release all
> fine - nice fast response in the X11 windows, with the Dec 16th release
> same programs in X11 windows are really, really slow.
> I can roll cygwin back to 3.0.7-1 from the latter release and X.11 then
> fine again.
> To quantify the problem, I timed these using the BeyondCompare and kdiff3
> file diff programs (which really show up the issue being very CPU
> comparing two versions of a source code directory containing 6 largish
> all differing:
> Time to open the window and display the directory:
> BeyondCompare with cygwin 3.0.7-1:	2 seconds, 	with cygwin 3.1.0-1:
> 	18 seconds.
> Kdiff3 with cygwin		4 seconds 	with cygwin 3.1.0-1:
> 	15 seconds.
> Time to open a tab and display the diffs for one of the files:
> BeyondCompare with cygwin 3.0.7-1:	1 seconds, 	with cygwin 3.1.0-1:
> 	8 seconds.
> Kdiff3 with cygwin		5 seconds 	with cygwin 3.1.0-1:
> 	13 seconds.
> Firefox is not so bad, but still slower. The time to open the window and
> display the default home page is about 2 seconds with cygwin 3.0.7-1, 5
> seconds with 3.1.0-1. And the problem that I reported below relating to
> response trying to type into Firefox's address bar is not showing up with
> build. Either that was introduced later, or maybe it was some side effect
> the upgrade path that I took then?
> Ian
> > -----Original Message-----
> > From: <> On
> Behalf Of
> > Ian Puleston
> > Sent: Friday, December 27, 2019 4:39 PM
> >
> > Hi,
> >
> > I have a Cygwin installation on a Windows 10 PC, on which I use
> > X-Windows to access a Linux development/build server. All has been
> > working great for a long time, until I rand a Cygwin upgrade on
> > December 23rd, and after that
> > X11 has become pretty much unusable. I normally launch the terminator
> > terminal emulator locally under X, in that I "ssh -Y" to the Linux
> > machine, and then on there I use a number of GUI apps, mainly
> > SlickEdit and BeyondCompare, which run remotely via X11 forwarding to
> > display in windows on my local Windows PC. But since this Cygwin
> > upgrade all of those remote X11 apps are now extremely slow to respond
> > to anything - about 10 to 20 seconds to action any key press or mouse
> click.
> >
> > The two machines are on the same Gig-Ethernet LAN segment so there are
> > no latency issues there (ping response time <1mS).
> >
> > To take any possible problems with those components out of the
> > picture, I tried instead launching xterm under X11 locally, and from
> > it launching Firefox after ssh to the Linux machine, and again I see
> > the same symptoms with that
> > - trying to type into Firefox's address bar takes about 10 seconds per
> >
> > I had previously updated my Cygwin installation on March 3rd 2019, so
> > this problem has come in sometime between then and now. I've just
> > spent a very long day and a half rolling back the changes as much as I
> > could (by hacking the setup.ini and re-installing previous versions
> > from the local download
> > cache) and eventually managed to get a working hybrid with enough
> > packages rolled back to make the difference, and now X11 is working
> > fine again.
> >
> > I also tried a new clean install of the latest Cygwin, after deleting
> > my .XWinrc and removing all but the bare minimum from .startxwinrc,
> > and do see the problem with that too.
> >
> > Is this any known problem? I couldn't find anything obvious in the
> > email archives.
> >
> > Ian
> >
> > --
> > Problem reports:
> > FAQ:         
> > Documentation:
> > Unsubscribe info:

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