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

[Corinna Vinschen]

[Move discussion to cygwin-developers]

On Aug 30 17:02, Takashi Yano via Cygwin wrote:
> On Sun, 29 Aug 2021 22:15:29 -0400
> Ken Brown wrote:
> > On 8/29/2021 8:22 PM, Takashi Yano via Cygwin wrote:
> > > We have two easy options:
> > > 1) Configure the pipe with PIPE_ACCESS_DUPLEX.
> > > 2) Use nt_create() again and forget C# program issue.
> > 
> > I vote for 2), but let's see what Corinna thinks.
> 
> BTW. what's wrong if just:
> 
> static int
> nt_create (LPSECURITY_ATTRIBUTES sa_ptr, PHANDLE r, PHANDLE w,
>                 DWORD psize, int64_t *unique_id)
> {
>   if (r && w)
>     {
>       static volatile ULONG pipe_unique_id;
>       LONG id = InterlockedIncrement ((LONG *) &pipe_unique_id);
>       if (unique_id)
>         *unique_id = ((int64_t) id << 32 | GetCurrentProcessId ());
>       if (!CreatePipe (r, w, sa_ptr, psize))
>         {
>           *r = *w = NULL;
>           return GetLastError ();
>         }
>     }
>   return 0;
> }
> 
> ?
> 
> In my environment, I cannot find any defects.
> - No performance degradation.
> - set_pipe_non_blocking() works for both read and write pipes.
> - NtQueryInformationFile() in select() works for both r/w pipes.
> - Piping C# program works.
> 
> Is naming the pipe really necessary?

It's not, but CreatePipe is doing this anyway.

"Anonymous pipes are implemented using a named pipe with a unique name."
https://docs.microsoft.com/en-us/windows/win32/api/namedpipeapi/nf-namedpipeapi-createpipe

The reason CreateNamedPipe was used in the first place was that
FILE_READ_ATTRIBUTES isn't set by CreatePipe for the write side
of the pipe, however, it creates full duplex pipe:

https://cygwin.com/pipermail/cygwin-patches/2004q3/004912.html

Given the fact that CreatePipe is implemented in terms of
NtCreateNamedPipeFile anyway, why should the pipe created with
NtCreateNamedPipeFile fail where the pipe created with CreatePipe works?

The only reason can be some missing flag, I think.  Checking
fhandler_pipe.cc::nt_create and comparing that with the default flags
for files and other devices, it occurs to me that the SYNCHRONIZE stuff
is missing.  So, Takashi, what if you call NtCreateNamedPipeFile like
this in nt_create:

  status = NtCreateNamedPipeFile (r, access | SYNCHRONIZE, &attr, &io,
				  FILE_SHARE_READ | FILE_SHARE_WRITE,
				  FILE_CREATE, FILE_SYNCHRONOUS_IO_NONALERT,
				  pipe_type, FILE_PIPE_BYTE_STREAM_MODE,
				  0, 1, psize, psize, &timeout);

Does that fix the above problems, too?


Corinna