X-Recipient:	archive-cygwin AT delorie DOT com
DKIM-Filter:	OpenDKIM Filter v2.11.0 sourceware.org 59FD73858428
DKIM-Signature:	v=1; a=rsa-sha256; c=relaxed/relaxed; d=cygwin.com;
	s=default; t=1630283040;
	bh=tlodkB+LIJniZPfmqMtS+CULtDgFztNPYYbjAsyNwlU=;
	h=Date:To:Subject:In-Reply-To:References:List-Id:List-Unsubscribe:
	List-Archive:List-Post:List-Help:List-Subscribe:From:Reply-To:
	From;
	b=AT2NzOxU07c3WJSB578dEWgn5WVG7ZyJnK2rHo2iy+vlzuKKG6HkjLeDOggk40qz3
	exnmH/3SyHX4bejFsEOMijJIEDc3i6De+kVcaHQa9YP78xA0b2ngm7wvnhvj/H4SKt
	rrIYnJ12OVltRfbdcjA+DY6+rNW7i0UiVoMK0wqk=
X-Original-To:	cygwin AT cygwin DOT com
Delivered-To:	cygwin AT cygwin DOT com
DMARC-Filter:	OpenDMARC Filter v1.4.1 sourceware.org AC2BC3858C3B
DKIM-Filter:	OpenDKIM Filter v2.10.3 conssluserg-04.nifty.com 17U0Mp92028626
X-Nifty-SrcIP:	[110.4.221.123]
Date:	Mon, 30 Aug 2021 09:22:59 +0900
To:	cygwin AT cygwin DOT com
Subject:	Re: cygrunsrv + sshd + rsync = 20 times too slow -- throttled?
Message-Id:	<20210830092259.52f7d54fc3fa340738373af4@nifty.ne.jp>
In-Reply-To:	<20210830091314.f9a2cb71794d0f68cdb5eba7@nifty.ne.jp>
References:	<41A583E1-C8E7-42AB-9F24-EEC33A41EC60 AT house DOT org>
	<20210825201845 DOT 07b6400b79dc5558a7761efe AT nifty DOT ne DOT jp>
	<f8106fe7-a2b8-d106-3061-4d888124f4b0 AT cornell DOT edu>
	<20210826062934 DOT 54f2f2216021c095bb7ba13b AT nifty DOT ne DOT jp>
	<d0a8c57d-1ed1-6b4f-c6e7-cbe0e2ec8a1c AT cornell DOT edu>
	<3b560051-ab27-f392-ca4b-d1fd9b5733b0 AT cornell DOT edu>
	<20210827202440 DOT 47706fc2fc07c5e9a1bc0047 AT nifty DOT ne DOT jp>
	<4f2cb5f3-ce9c-c617-f65f-841a5eca096e AT cornell DOT edu>
	<20210828022111 DOT 91ef5b4ff24f6da9fadb489e AT nifty DOT ne DOT jp>
	<YSn3L0W1M527utK0 AT calimero DOT vinschen DOT de>
	<20210828184102 DOT f2206a8a9e5fe5cf24bf5e45 AT nifty DOT ne DOT jp>
	<20210829180729 DOT 48b4e877f773cb3980c5766d AT nifty DOT ne DOT jp>
	<c62d18df-ab7a-7233-62ee-29a8eced5353 AT cornell DOT edu>
	<20210830091314 DOT f9a2cb71794d0f68cdb5eba7 AT nifty DOT ne DOT jp>
X-Mailer:	Sylpheed 3.7.0 (GTK+ 2.24.30; i686-pc-mingw32)
Mime-Version:	1.0
X-Spam-Status:	No, score=-10.3 required=5.0 tests=BAYES_00, DKIM_SIGNED,
	DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, GIT_PATCH_0, NICE_REPLY_A,
	RCVD_IN_DNSWL_NONE, SPF_HELO_NONE, SPF_PASS,
	TXREP autolearn=ham autolearn_force=no version=3.4.4
X-Spam-Checker-Version:	SpamAssassin 3.4.4 (2020-01-24) on
	server2.sourceware.org
X-BeenThere:	cygwin AT cygwin DOT com
X-Mailman-Version:	2.1.29
List-Id:	General Cygwin discussions and problem reports <cygwin.cygwin.com>
List-Unsubscribe:	<https://cygwin.com/mailman/options/cygwin>,
	<mailto:cygwin-request AT cygwin DOT com?subject=unsubscribe>
List-Archive:	<https://cygwin.com/pipermail/cygwin/>
List-Post:	<mailto:cygwin AT cygwin DOT com>
List-Help:	<mailto:cygwin-request AT cygwin DOT com?subject=help>
List-Subscribe:	<https://cygwin.com/mailman/listinfo/cygwin>,
	<mailto:cygwin-request AT cygwin DOT com?subject=subscribe>
From:	Takashi Yano via Cygwin <cygwin AT cygwin DOT com>
Reply-To:	Takashi Yano <takashi DOT yano AT nifty DOT ne DOT jp>
Errors-To:	cygwin-bounces+archive-cygwin=delorie DOT com AT cygwin DOT com
Sender:	"Cygwin" <cygwin-bounces+archive-cygwin=delorie DOT com AT cygwin DOT com>

On Mon, 30 Aug 2021 09:13:14 +0900
Takashi Yano wrote:
> On Sun, 29 Aug 2021 17:04:56 -0400
> Ken Brown wrote:
> > On 8/29/2021 5:07 AM, Takashi Yano via Cygwin wrote:
> > > On Sat, 28 Aug 2021 18:41:02 +0900
> > > Takashi Yano wrote:
> > >> On Sat, 28 Aug 2021 10:43:27 +0200
> > >> Corinna Vinschen wrote:
> > >>> On Aug 28 02:21, Takashi Yano via Cygwin wrote:
> > >>>> On Fri, 27 Aug 2021 12:00:50 -0400
> > >>>> Ken Brown wrote:
> > >>>>> 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.
> > >>>
> > >>> The problem is this:
> > >>>
> > >>>    if (PeekNamedPipe())
> > >>>      ReadFile(blocking);
> > >>>
> > >>> is not atomic.  I. e., if PeekNamedPipe succeeds, nothing keeps another
> > >>> thread from draining the pipe between the PeekNamedPipe and the ReadFile
> > >>> call.  And as soon as ReadFile runs, it hangs indefinitely and we can't
> > >>> stop it via a signal.
> > >>
> > >> Hmm, you are right. Mutex guard seems to be necessary like pty code
> > >> if we go this way.
> > > 
> > > I have found that set_pipe_non_blocking() succeeds for both read and
> > > write pipes if the write pipe is created by CreateNamedPipe() and the
> > > read pipe is created by CreateFile() contrary to the current create()
> > > code. Therefore, not only nt_create() but also PeekNamedPipe() become
> > > unnecessary.
> > > 
> > > Please see the revised patch attached.
> > 
> > I haven't had a chance to test this myself yet, but occurs to me that we might 
> > have a different problem after this patch: Does the write handle that we get 
> > from CreateNamedPipe() have FILE_READ_ATTRIBUTES access?
> 
> I have just checked this, and the answer is "No". Due to this problem,
> NtQueryInformationFile() call in select() fails on the write pipe.
> 
> It seems that we need more consideration...

We have two easy options:
1) Configure the pipe with PIPE_ACCESS_DUPLEX.
2) Use nt_create() again and forget C# program issue.



Even without this problem, select() for writing pipe has a bug
and does not wrok as expected. The following patch seems to be
needed.

diff --git a/winsup/cygwin/select.cc b/winsup/cygwin/select.cc
index 83e1c00e0..ac2fd227e 100644
--- a/winsup/cygwin/select.cc
+++ b/winsup/cygwin/select.cc
@@ -612,7 +612,6 @@ pipe_data_available (int fd, fhandler_base *fh, HANDLE h, bool writing)
           that.  This means that a pipe could still block since you could
           be trying to write more to the pipe than is available in the
           buffer but that is the hazard of select().  */
-      fpli.WriteQuotaAvailable = fpli.OutboundQuota - fpli.ReadDataAvailable;
       if (fpli.WriteQuotaAvailable > 0)
        {
          paranoid_printf ("fd %d, %s, write: size %u, avail %u", fd,

-- 
Takashi Yano <takashi DOT yano AT nifty DOT ne DOT jp>

-- 
Problem reports:      https://cygwin.com/problems.html
FAQ:                  https://cygwin.com/faq/
Documentation:        https://cygwin.com/docs.html
Unsubscribe info:     https://cygwin.com/ml/#unsubscribe-simple

- Raw text -