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

[Ken Brown]

On 9/12/2021 2:23 AM, Takashi Yano wrote:
> On Sat, 11 Sep 2021 09:12:02 -0400
> Ken Brown wrote:
>> On 9/10/2021 10:35 PM, Takashi Yano wrote:
>>> On Fri, 10 Sep 2021 22:17:21 -0400
>>> Ken Brown wrote:
>>>> On 9/10/2021 6:57 PM, Takashi Yano wrote:
>>>>> On Fri, 10 Sep 2021 11:17:58 -0400
>>>>> Ken Brown wrote:
>>>>>> I've rerun your test with the latest version, and the test results are similar.
>>>>>>      I've also run a suite of fifo tests that I've accumulated, and they all pass
>>>>>> also, so I pushed your patch.
>>>>>>
>>>>>> I think we're in pretty good shape now.  The only detail remaining, AFAIK, is
>>>>>> how to best avoid a deadlock if the pipe has been created by a non-Cygwin
>>>>>> process.  I've proposed a timeout, but maybe there's a better idea.
>>>>>
>>>>> I am not pretty sure what is the problem, but is not the following
>>>>> patch enough?
>>>>>
>>>>> diff --git a/winsup/cygwin/fhandler.h b/winsup/cygwin/fhandler.h
>>>>> index d309be2f7..13fba9a14 100644
>>>>> --- a/winsup/cygwin/fhandler.h
>>>>> +++ b/winsup/cygwin/fhandler.h
>>>>> @@ -1205,6 +1205,7 @@ public:
>>>>>       select_record *select_except (select_stuff *);
>>>>>       char *get_proc_fd_name (char *buf);
>>>>>       int open (int flags, mode_t mode = 0);
>>>>> +  void open_setup (int flags);
>>>>>       void fixup_after_fork (HANDLE);
>>>>>       int dup (fhandler_base *child, int);
>>>>>       int close ();
>>>>> diff --git a/winsup/cygwin/fhandler_pipe.cc b/winsup/cygwin/fhandler_pipe.cc
>>>>> index 6994a5dce..d84e6ad84 100644
>>>>> --- a/winsup/cygwin/fhandler_pipe.cc
>>>>> +++ b/winsup/cygwin/fhandler_pipe.cc
>>>>> @@ -191,6 +191,17 @@ out:
>>>>>       return 0;
>>>>>     }
>>>>>
>>>>> +void
>>>>> +fhandler_pipe::open_setup (int flags)
>>>>> +{
>>>>> +  fhandler_base::open_setup (flags);
>>>>> +  if (get_dev () == FH_PIPER && !read_mtx)
>>>>> +    {
>>>>> +      SECURITY_ATTRIBUTES *sa = sec_none_cloexec (flags);
>>>>> +      read_mtx = CreateMutexW (sa, FALSE, NULL);
>>>>> +    }
>>>>> +}
>>>>> +
>>>>>     off_t
>>>>>     fhandler_pipe::lseek (off_t offset, int whence)
>>>>>     {
>>>>>
>>>>>
>>>>> AFAIK, another problem remaining is:
>>>>>
>>>>> On Mon, 6 Sep 2021 14:49:55 +0200
>>>>> Corinna Vinschen wrote:
>>>>>> - What about calling select for writing on pipes read by non-Cygwin
>>>>>>      processes?  In that case, we still can't rely on WriteQuotaAvailable,
>>>>>>      just as before.
>>>>
>>>> This is the problem I was talking about.  In this case the non-Cygwin process
>>>> might have a large pending read, so that the Cygwin process calling select on
>>>> the write side will see WriteQuotaAvailable == 0.  This could lead to a deadlock
>>>> with the Cygwin process waiting for write ready while the non-Cygwin process is
>>>> blocked trying to read.
>>>
>>> Then, the above patch is for another issue.
>>> The problem happes when:
>>> 1) Start command prompt.
>>> 2) Run 'echo AAAAAAAAAAAA | \cygwin64\bin\cat
>>> This causes hang up in cat. In this case, pipe is created by cmd.exe.
>>> Therefore, read_mtx is not created.
>>
>> Confirmed, and your patch fixes it.  Maybe you should check for error in the
>> call to CreateMutexW and print a debug message in that case.
> 
> I added the debug message.

LGTM.

Ken