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| Subject: | Re: cygrunsrv + sshd + rsync = 20 times too slow -- throttled? |
| From: | Chris Roehrig <croehrig AT house DOT org> |
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| Date: | Wed, 25 Aug 2021 11:51:58 -0700 |
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It looks like there was a previous (2013) patch and attempt to add a pipe_nooverlap CYGWIN option that was rejected by the maintainers: https://stackoverflow.com/questions/10385424/good-alternatives-to-cygwin-cygwin-doesnt-support-natively-support-win32-app Is this something that can be revisited? It seems to be affecting pure-UNIX situations (in my case) which is Cygwin's core audience. - Chris On Wed Aug 25 2021, at 11:18 AM, Chris Roehrig <croehrig AT house DOT org> wrote: > On Wed Aug 25 2021, at 10:52 AM, Ken Brown via Cygwin <cygwin AT cygwin DOT 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 $WINHOST md5sum >>>> I also get the full 100 MB/s transfers, so it doesn't look like sshd itself is being throttled by bandwidth or CPU. >>>> >>>> The machines have less than 15% CPU utilization while transferring, with each of the 4 cores less than 30%, so it doesn't look to be CPU issue. >>>> In Task Manager, sshd.exe and rsync.exe seem to be running normally using only few percent CPU, and show Power Throttling=Disabled, Priority=Normal. Setting their Priority to High doesn't seem to change things. >>>> >>>> Looking in Resource Monitor on the remote endpoint, the network usage is pretty much a flat horizontal line at about 18 Mbps (2.5 MB/s), so it sure looks to me as if rsync is somehow being bandwidth-throttled when run in the background under cygsshd. >>>> >>>> It's almost as if rsync has an implicit --bwlimit override when it is run from cygrunsrv+sshd (I've tried --bwlimit=0 on the client which makes no difference). >>>> >>>> >>>> Any ideas? Not sure where to go from here. >>> In cygwin, just scp is very slow. >>> The transfer speed in my environment is as follows. >>> The tests were done with 100MB of test.dat file. >>> (1-1) From cygwin-PC, >>> [yano AT cygwin-PC ~]$ 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. >> >> >> >> -- >> 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 -- 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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