On Wed Aug 25 2021, at 10:52 AM, Ken Brown via Cygwin <cygwin@cygwin.com> wrote: > A couple years ago I had an idea for changing the pipe implementation to > avoid overlapped I/O: > > https://cygwin.com/pipermail/cygwin-patches/2019q2/009393.html > https://cygwin.com/pipermail/cygwin-patches/2019q2/009423.html > > I never followed up on it. But if you think it might help with this problem, > I could dust it off and try to finish it. > > Ken
I'm not familiar enough with the innards of rsync, sshd or cygwin to know how this would work. Is it possible to have a new CYGWIN environment option to switch the pipe behaviour without requiring changes to the ssh or rsync source code (and without breaking any existing stuff)? - Chris > On 8/25/2021 7:18 AM, Takashi Yano via Cygwin wrote: >> On Tue, 24 Aug 2021 12:49:52 -0700 >> Chris Roehrig wrote: >>> I have a network of Windows, Linux and Mac machines and I use rsync to >>> synchronize various directories between them. >>> >>> I'm trying to figure out why my rsync transfers are so slow (<4 MB/s) only >>> when the remote endpoint is Cygwin rsync over sshd (with both a Linux or >>> Cygwin rsync client). In all other scenarios, I get the full 100MB/s as >>> expected from gigabit ethernet. This has been an ongoing problem for me >>> for a couple of years over several Windows and Cygwin versions, and I'd >>> like to try to fix it. >>> >>> If I run rsync --daemon --no-detach under mintty in the foreground on the >>> remote Windows endpoint, I get the full 100 MB/s transfers, so it seems >>> like it has something to do with rsync.exe running in the background under >>> the cygrunsrv+sshd service (which was installed normally using >>> ssh-host-config). >>> >>> If I do: >>> pv /dev/zero | ssh $WINHOST "cat > /dev/null" >>> or even >>> pv /dev/urandom | ssh $WINHOST md5sum >>> I also get the full 100 MB/s transfers, so it doesn't look like sshd itself >>> is being throttled by bandwidth or CPU. >>> >>> The machines have less than 15% CPU utilization while transferring, with >>> each of the 4 cores less than 30%, so it doesn't look to be CPU issue. >>> In Task Manager, sshd.exe and rsync.exe seem to be running normally using >>> only few percent CPU, and show Power Throttling=Disabled, Priority=Normal. >>> Setting their Priority to High doesn't seem to change things. >>> >>> Looking in Resource Monitor on the remote endpoint, the network usage is >>> pretty much a flat horizontal line at about 18 Mbps (2.5 MB/s), so it sure >>> looks to me as if rsync is somehow being bandwidth-throttled when run in >>> the background under cygsshd. >>> >>> It's almost as if rsync has an implicit --bwlimit override when it is run >>> from cygrunsrv+sshd (I've tried --bwlimit=0 on the client which makes no >>> difference). >>> >>> >>> Any ideas? Not sure where to go from here. >> In cygwin, just scp is very slow. >> The transfer speed in my environment is as follows. >> The tests were done with 100MB of test.dat file. >> (1-1) From cygwin-PC, >> [yano@cygwin-PC ~]$ scp test.dat yano@linux-server:. >> yano@linux-server's password: >> test.dat 100% 100MB 4.0MB/s 00:24 >> [yano@cygwin-PC ~]$ scp yano@linux-server:test.dat . >> yano@linux-server's password: >> test.dat 100% 100MB 8.0MB/s 00:12 >> (1-2) From linux-server, >> yano@linux-server:~$ scp yano@cygwin-PC:test.dat . >> yano@cygwin-PC's password: >> test.dat 100% 100MB 4.0MB/s 00:24 >> yano@linux-server:~$ scp test.dat yano@cygwin-PC:. >> yano@cygwin-PC's password: >> test.dat 100% 100MB 4.1MB/s 00:24 >> I looked into this problem, and noticed that this is caused >> by cygwin pipe implementation. Pipe in cygwin is configured >> with FILE_FLAG_OVERLAPPED. >> If the pipe is configured without FILE_FLAG_OVERLAPPED, >> the transfer speed is much improved as follows. >> (2-1) From cygwin-PC, >> [yano@cygwin-PC ~]$ scp test.dat yano@linux-server:. >> yano@linux-server's password: >> test.dat 100% 100MB 85.5MB/s 00:01 >> [yano@cygwin-PC ~]$ scp yano@linux-server:test.dat . >> yano@linux-server's password: >> test.dat 100% 100MB 69.7MB/s 00:01 >> (2-2) From linux-server, >> yano@linux-server:~$ scp yano@cygwin-PC:test.dat . >> yano@cygwin-PC's password: >> test.dat 100% 100MB 80.1MB/s 00:01 >> yano@linux-server:~$ scp test.dat yano@cygwin-PC:. >> yano@cygwin-PC's password: >> test.dat 100% 100MB 57.7MB/s 00:01 >> I am not sure why this happens and how to fix this. > > > > -- > Problem reports: https://cygwin.com/problems.html > FAQ: https://cygwin.com/faq/ > Documentation: https://cygwin.com/docs.html > Unsubscribe info: https://cygwin.com/ml/#unsubscribe-simple -- Problem reports: https://cygwin.com/problems.html FAQ: https://cygwin.com/faq/ Documentation: https://cygwin.com/docs.html Unsubscribe info: https://cygwin.com/ml/#unsubscribe-simple
