The FILE_FLAG_OVERLAPPED avenue looks promising. I get exactly the same results as you using 'scp': 4MB/s in either direction (with either remote endpoint.)
I guess the next step is to install a build environment and build rsync and sshd ... On Wed Aug 25 2021, at 4:18 AM, Takashi Yano via Cygwin <cygwin@cygwin.com> 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. > Any idea? > > -- > Takashi Yano <takashi.y...@nifty.ne.jp> > > -- > 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