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 22:15:29 -0400 [thread overview]
Message-ID: <d217ef03-7858-5e22-0aa6-f0507eedd9da@cornell.edu> (raw)
In-Reply-To: <20210830092259.52f7d54fc3fa340738373af4@nifty.ne.jp>
On 8/29/2021 8:22 PM, Takashi Yano via Cygwin wrote:
> 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.
I vote for 2), but let's see what Corinna thinks.
> 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,
>
I agree.
Ken
next prev parent reply other threads:[~2021-08-30 2:15 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
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 [this message]
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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