From: Ken Brown <kbrown@cornell.edu>
To: cygwin@cygwin.com
Subject: Re: cygrunsrv + sshd + rsync = 20 times too slow -- throttled?
Date: Sun, 29 Aug 2021 18:42:06 -0400 [thread overview]
Message-ID: <6e9bb35e-6f4f-cf78-e515-549da487b5ef@cornell.edu> (raw)
In-Reply-To: <20210829174124.0c1ae6c16a3e8da1f490abc7@nifty.ne.jp>
On 8/29/2021 4:41 AM, Takashi Yano wrote:
> Hi Ken,
>
> On Sat, 28 Aug 2021 16:55:52 -0400
> Ken Brown wrote:
>> On 8/28/2021 11:43 AM, Takashi Yano via Cygwin wrote:
>>> On Sat, 28 Aug 2021 13:58:08 +0200
>>> Corinna Vinschen wrote:
>>>> On Aug 28 18:41, Takashi Yano via Cygwin 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.
>>>>>
>>>>>> Is a blocking ReadFile actually faster than a non-blocking read? Or
>>>>>> does it mainly depend on BYTE vs. MESSAGE mode?
>>>>>
>>>>> Actually, I don't think so. Perhaps it is not essential problem of
>>>>> overlapped I/O but something is wrong with current pipe code.
>>>>>
>>>>>> What if the pipe is created non-blocking and stays non-blocking all the
>>>>>> time and uses BYTE mode all the time? Just as sockets, it would always
>>>>>> only emulate blocking mode. Wouldn't that drop code size a lot and fix
>>>>>> most problems?
>>>>>
>>>>> If 'non-blocking' means overlapped I/O, only the problem will be:
>>>>> https://cygwin.com/pipermail/cygwin/2021-March/247987.html
>>>>
>>>> Sorry if that wasn't clear, but I was not talking about overlapped I/O,
>>>> which we should get rid off, but of real non-blocking mode, which
>>>> Windows pipes are fortunately capable of.
>>>
>>> Do you mean, PIPE_NOWAIT flag? If this flags is specified in
>>> the read pipe, non-cygwin apps cannot read the pipe correctly.
>>
>> While waiting for Corinna's response to this, I have one more question. Do you
>> understand why nt_create() failed and you had to revert to create()? Was it an
>> access problem because nt_create requested FILE_WRITE_ATTRIBUTES? Or did I make
>> some careless mistake in writing nt_create?
>
> I am sorry but no. I don't understand why piping C# program via
> the pipe created by nt_create() has the issue. I tried to change
> setup parameters in nt_create(), however, I did not succeed it to
> work. I also couldn't find any mistake in nt_create() so far.
>
> Win32 programs which use ReadFile() and WriteFile() work even
> with the pipe created by nt_create() as well as overlapped I/O.
>
> What does C# program differ from legacy win32 program at all?
I don't know.
By the way, when I introduced nt_create(), my preference would have been to
simply change create() to use the NT API, but I was afraid to do that because I
didn't want to take a chance on breaking something. That's still my preference,
if we can find a way to work around this problem with C# programs.
Ken
next prev parent reply other threads:[~2021-08-29 22:42 UTC|newest]
Thread overview: 86+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-24 19:49 Chris Roehrig
2021-08-24 23:43 ` Mark Geisert
2021-08-25 0:35 ` Chris Roehrig
2021-08-25 2:12 ` Chris Roehrig
2021-08-25 2:02 ` NightStrike
2021-08-25 3:20 ` Mark Geisert
2021-08-25 17:24 ` Chris Roehrig
2021-08-25 11:18 ` Takashi Yano
2021-08-25 17:31 ` Chris Roehrig
2021-08-25 17:52 ` Ken Brown
2021-08-25 18:18 ` Chris Roehrig
2021-08-25 18:51 ` Chris Roehrig
2021-08-26 15:44 ` Ken Brown
2021-08-25 20:33 ` Mario Emmenlauer
2021-08-26 15:47 ` Ken Brown
2021-08-25 21:29 ` Takashi Yano
2021-08-26 15:56 ` Ken Brown
2021-08-26 22:18 ` Ken Brown
2021-08-27 11:24 ` Takashi Yano
2021-08-27 16:00 ` Ken Brown
2021-08-27 17:21 ` Takashi Yano
2021-08-28 2:00 ` Takashi Yano
2021-08-28 3:03 ` Takashi Yano
2021-08-28 8:43 ` Corinna Vinschen
2021-08-28 9:41 ` Takashi Yano
2021-08-28 11:58 ` Corinna Vinschen
2021-08-28 15:43 ` Takashi Yano
2021-08-28 20:55 ` Ken Brown
2021-08-29 8:41 ` Takashi Yano
2021-08-29 22:42 ` Ken Brown [this message]
2021-08-29 10:27 ` Corinna Vinschen
2021-08-29 9:07 ` Takashi Yano
2021-08-29 15:57 ` Ken Brown
2021-08-29 19:24 ` Chris Roehrig
2021-08-29 22:24 ` Ken Brown
2021-08-30 23:58 ` Chris Roehrig
2021-08-31 19:05 ` Ken Brown
2021-08-31 19:53 ` Chris Roehrig
2021-08-31 20:23 ` Chris Roehrig
2021-08-31 21:29 ` Brian Inglis
2021-09-01 21:11 ` Chris Roehrig
2021-09-02 15:25 ` Ken Brown
2021-09-02 19:03 ` Chris Roehrig
2021-09-03 17:26 ` Ken Brown
2021-09-03 19:55 ` Corinna Vinschen
2021-09-03 20:59 ` Chris Roehrig
2021-09-04 8:32 ` Achim Gratz
2021-09-04 16:45 ` Brian Inglis
2021-09-05 8:18 ` Achim Gratz
2021-09-05 15:11 ` Brian Inglis
2021-09-06 10:42 ` Achim Gratz
2021-09-04 22:37 ` mmap failure [was: cygrunsrv + sshd + rsync = 20 times too slow -- throttled?] Ken Brown
2021-09-04 22:54 ` Ken Brown
2021-09-04 22:58 ` Ken Brown
2021-09-05 0:04 ` Ken Brown
2021-09-05 13:24 ` Ken Brown
2021-09-06 15:32 ` Corinna Vinschen
2021-09-06 17:12 ` Ken Brown
2021-09-06 17:38 ` Ken Brown
2021-09-06 17:43 ` Eliot Moss
2021-09-06 17:59 ` Corinna Vinschen
2021-09-06 18:07 ` Corinna Vinschen
2021-09-06 18:40 ` Ken Brown
2021-09-06 20:52 ` Peter Dons Tychsen
2021-09-06 20:54 ` Peter Dons Tychsen
2021-09-06 21:24 ` Ken Brown
2021-09-06 21:31 ` Ken Brown
2021-09-07 3:34 ` Brian Inglis
2021-09-07 16:28 ` Ken Brown
2021-09-07 21:52 ` Lavrentiev, Anton (NIH/NLM/NCBI) [C]
2021-09-07 22:44 ` Ken Brown
2021-09-08 6:14 ` Sam Edge
2021-09-08 8:18 ` Corinna Vinschen
2021-09-07 21:41 ` Peter Dons Tychsen
2021-09-04 23:18 ` Brian Inglis
2021-08-29 19:37 ` cygrunsrv + sshd + rsync = 20 times too slow -- throttled? Takashi Yano
2021-08-29 21:09 ` Ken Brown
2021-08-29 21:04 ` Ken Brown
2021-08-30 0:13 ` Takashi Yano
2021-08-30 0:22 ` Takashi Yano
2021-08-30 2:15 ` Ken Brown
2021-08-30 8:02 ` Takashi Yano
2021-08-28 15:17 ` Ken Brown
2021-09-16 22:00 ` Keith Christian
2021-09-16 22:48 ` Ken Brown
2021-09-16 22:58 ` Keith Christian
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