On Wed, 25 Aug 2021 13:52:19 -0400 Ken Brown wrote: > 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. > > 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.
Interesting. It will be also helpfull for: https://cygwin.com/pipermail/cygwin/2021-March/247987.html which seems to be the same issue with https://stackoverflow.com/questions/10385424/good-alternatives-to-cygwin-cygwin-doesnt-support-natively-support-win32-app However, I wonder why scp dislikes overlapped I/O. -- 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
