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| Subject: | Re: cygrunsrv + sshd + rsync = 20 times too slow -- throttled? |
| From: | Chris Roehrig <chris AT islandmacguy DOT com> |
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| Date: | Wed, 25 Aug 2021 10:31:52 -0700 |
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| To: | Takashi Yano <takashi DOT yano AT nifty DOT ne DOT jp> |
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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 AT cygwin DOT 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 $WINHOST md5sum >> I also get the full 100 MB/s transfers, so it doesn't look like sshd itself is being throttled by bandwidth or CPU. >> >> The machines have less than 15% CPU utilization while transferring, with each of the 4 cores less than 30%, so it doesn't look to be CPU issue. >> In Task Manager, sshd.exe and rsync.exe seem to be running normally using only few percent CPU, and show Power Throttling=Disabled, Priority=Normal. Setting their Priority to High doesn't seem to change things. >> >> Looking in Resource Monitor on the remote endpoint, the network usage is pretty much a flat horizontal line at about 18 Mbps (2.5 MB/s), so it sure looks to me as if rsync is somehow being bandwidth-throttled when run in the background under cygsshd. >> >> It's almost as if rsync has an implicit --bwlimit override when it is run from cygrunsrv+sshd (I've tried --bwlimit=0 on the client which makes no difference). >> >> >> Any ideas? Not sure where to go from here. > > In cygwin, just scp is very slow. > > The transfer speed in my environment is as follows. > The tests were done with 100MB of test.dat file. > > (1-1) From cygwin-PC, > [yano AT cygwin-PC ~]$ scp test.dat yano AT linux-server:. > yano AT linux-server's password: > test.dat 100% 100MB 4.0MB/s 00:24 > [yano AT cygwin-PC ~]$ scp yano AT linux-server:test.dat . > yano AT linux-server's password: > test.dat 100% 100MB 8.0MB/s 00:12 > > (1-2) From linux-server, > yano AT linux-server:~$ scp yano AT cygwin-PC:test.dat . > yano AT cygwin-PC's password: > test.dat 100% 100MB 4.0MB/s 00:24 > yano AT linux-server:~$ scp test.dat yano AT cygwin-PC:. > yano AT 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 AT cygwin-PC ~]$ scp test.dat yano AT linux-server:. > yano AT linux-server's password: > test.dat 100% 100MB 85.5MB/s 00:01 > [yano AT cygwin-PC ~]$ scp yano AT linux-server:test.dat . > yano AT linux-server's password: > test.dat 100% 100MB 69.7MB/s 00:01 > > (2-2) From linux-server, > yano AT linux-server:~$ scp yano AT cygwin-PC:test.dat . > yano AT cygwin-PC's password: > test.dat 100% 100MB 80.1MB/s 00:01 > yano AT linux-server:~$ scp test.dat yano AT cygwin-PC:. > yano AT 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 DOT yano AT nifty DOT ne DOT 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
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