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

[Ken Brown]

On 8/31/2021 1:30 PM, Corinna Vinschen wrote:
> On Aug 31 12:38, Ken Brown wrote:
>> And here's a really trivial comment about your patch to raw_write: Where you have
>>
>>    len1 = fpli.InboundQuota - fpli.ReadDataAvailable;
>>
>> I think the code would be slightly clearer if you wrote
>>
>>    len1 = fpli.WriteQuotaAvailable;
> 
> D'oh!  That was the idea.  Aparently I forgot it in mid-air...

One more thing.  For a non-blocking write, according to POSIX, "A write request 
for {PIPE_BUF} or fewer bytes shall have the following effect: if there is 
sufficient space available in the pipe, write() shall transfer all the data and 
return the number of bytes requested. Otherwise, write() shall transfer no data 
and return -1 with errno set to [EAGAIN]."

So I think the condition for breaking from the retry loop has to be changed from

   evt || !NT_SUCCESS (status) || io.Information > 0

to

   evt || !NT_SUCCESS (status) || io.Information > 0 || len <= PIPE_BUF

And I wonder if we've now uncovered a reason for using message mode: If the pipe 
was created in byte mode, might we get a partial write when len <= PIPE_BUF?  I 
see the following under "Pipes" at

   https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-writefile

"When writing to a non-blocking, byte-mode pipe handle with insufficient buffer 
space, WriteFile returns TRUE with *lpNumberOfBytesWritten < nNumberOfBytesToWrite."

Ken