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

[Corinna Vinschen]

On Sep 15 20:54, Takashi Yano wrote:
> This shoudl be:
> 
> @@ -652,11 +652,17 @@ pipe_data_available (int fd, fhandler_base *fh, HANDLE h, bool writing)
>  	}
>        /* TODO: Buffer really full or non-Cygwin reader? */
>      }
> -  else if (fpli.ReadDataAvailable)
> +  else
>      {
> -      paranoid_printf ("fd %d, %s, read avail %u", fd, fh->get_name (),
> -		       fpli.ReadDataAvailable);
> -      return 1;
> +      DWORD nbytes_in_pipe;
> +      if (PeekNamedPipe (h, NULL, 0, NULL, &nbytes_in_pipe, NULL))
> +	{
> +	  paranoid_printf ("fd %d, %s, read avail %u", fd, fh->get_name (),
> +			   nbytes_in_pipe);
> +	  return nbytes_in_pipe > 0;
> +	}
> +      else if (GetLastError () == ERROR_BROKEN_PIPE)
> +	return -1;
>      }
>    if (fpli.NamedPipeState & FILE_PIPE_CLOSING_STATE)
>      return -1;

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