cygrunsrv + sshd + rsync = 20 times too slow -- throttled?

[Takashi Yano]

On Fri, 27 Aug 2021 12:00:50 -0400
Ken Brown wrote:

> On 8/27/2021 7:24 AM, Takashi Yano wrote:
> > On Thu, 26 Aug 2021 18:18:29 -0400
> > Ken Brown wrote:
> >> On 8/26/2021 11:56 AM, Ken Brown via Cygwin wrote:
> [...]
> >> In case you want to try out my proposed change, I've just rebased the patches to
> >> the current master and pushed them to a new topic/pipe branch.
> > 
> > Hi Ken,
> > 
> > Thanks much! I tested topic/pipe branch.
> > 
> > [yano@cygwin-PC ~]$ scp test.dat yano@linux-server:.
> > yano@linux-server's password:
> > test.dat                                      100%  100MB  95.9MB/s   00:01
> > [yano@cygwin-PC ~]$ scp yano@linux-server:test.dat .
> > yano@linux-server's password:
> > test.dat                                      100%  100MB   8.0MB/s   00:12
> > 
> > yano@linux-server:~$ scp yano@cygwin-PC:test.dat .
> > yano@cygwin-PC's password:
> > test.dat                                      100%  100MB 109.7MB/s   00:00
> > yano@linux-server:~$ scp test.dat yano@cygwin-PC:.
> > yano@cygwin-PC's password:
> > test.dat                                      100%  100MB  31.4MB/s   00:03
> > 
> > As shown above, outgoing transfer-rate has been improved upto near
> > theoretical limit. However, incoming transfer-rate is not improved
> > much.
> > 
> > I digged further and found the first patch attached solves the issue
> > as follows.
> > 
> > [yano@cygwin-PC ~]$ scp yano@linux-server:test.dat .
> > yano@linux-server's password:
> > test.dat                                      100%  100MB 112.8MB/s   00:00
> > 
> > yano@linux-server2:~$ scp test.dat yano@cygwin-PC:.
> > yano@cygwin-PC's password:
> > test.dat                                      100%  100MB 102.5MB/s   00:00
> 
> Great!
> 
> > I also tested the case:
> >>>> 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
> > 
> > Unfortunately, topic/pipe does not help.
> > 
> > I confirmed that applying the second patch attached, which reverts
> > to create() rather than nt_create(), and setting CYGWIN=pipe_byte
> > fixes the problem.
> > 
> > What do you think of this alternative implementation which does
> > not use nt_create()?
> 
> Two years ago I thought I needed nt_create to avoid problems when calling 
> set_pipe_non_blocking.  Are you saying that's not an issue?  Is 
> set_pipe_non_blocking unnecessary?  Is that the point of your modification to 
> raw_read?

Yes. Instead of making windows read function itself non-blocking,
it is possible to check if the pipe can be read before read using
PeekNamedPipe(). If the pipe cannot be read right now, EAGAIN is
returned.

-- 
Takashi Yano <takashi.yano@nifty.ne.jp>