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

[Takashi Yano]

On Wed, 15 Sep 2021 14:20:48 +0200
Corinna Vinschen wrote:
> After Ken's comment, I was going to suggest this one:
> 
> From 34b14470406cb9551f98707bf63175811a506523 Mon Sep 17 00:00:00 2001
> From: Corinna Vinschen
> Date: Wed, 15 Sep 2021 14:17:59 +0200
> Subject: [PATCH] Cygwin: pipes: don't call NtQueryInformationFile on read side
>  of pipes
> 
> NtQueryInformationFile hangs if it's called on the read side handle of
> a pipe while another thread or process is performing a blocking read.
> 
> Avoid select potentially hanging by calling NtQueryInformationFile
> only on the write side of the pipe and using PeekNamedPipe otherwise.
> 
> ---
>  winsup/cygwin/select.cc | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/winsup/cygwin/select.cc b/winsup/cygwin/select.cc
> index a09d8a34da2e..566cf66d653b 100644
> --- a/winsup/cygwin/select.cc
> +++ b/winsup/cygwin/select.cc
> @@ -587,6 +587,14 @@ no_verify (select_record *, fd_set *, fd_set *, fd_set *)
>  static int
>  pipe_data_available (int fd, fhandler_base *fh, HANDLE h, bool writing)
>  {
> +  if (fh->get_device () == FH_PIPER)
> +    {
> +      DWORD nbytes_in_pipe;
> +      if (!writing && PeekNamedPipe (h, NULL, 0, NULL, &nbytes_in_pipe, NULL))
> +	return nbytes_in_pipe > 0;
> +      return -1;
> +    }
> +
>    IO_STATUS_BLOCK iosb = {{0}, 0};
>    FILE_PIPE_LOCAL_INFORMATION fpli = {0};
>    NTSTATUS status;
> -- 
> 2.31.1
> 

LGTM.
I also confirmed a several test cases are all passed with this patch.

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