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

[Ken Brown]

On 9/10/2021 6:57 AM, Ken Brown wrote:
> Hi Takashi,
> 
> On 9/9/2021 8:42 AM, Takashi Yano wrote:
>> On Thu, 9 Sep 2021 21:19:40 +0900
>> Takashi Yano wrote:
>>> On Thu, 9 Sep 2021 17:05:49 +0900
>>> Takashi Yano wrote:
>>>> On Thu, 9 Sep 2021 12:41:15 +0900
>>>> Takashi Yano wrote:
>>>>> diff --git a/winsup/cygwin/fhandler_fifo.cc b/winsup/cygwin/fhandler_fifo.cc
>>>>> index 6709fb974..c40573783 100644
>>>>> --- a/winsup/cygwin/fhandler_fifo.cc
>>>>> +++ b/winsup/cygwin/fhandler_fifo.cc
>>>>> @@ -1047,6 +1047,12 @@ writer_shmem:
>>>>>     ResetEvent (writer_opening);
>>>>>     nwriters_unlock ();
>>>>>   success:
>>>>> +  if (!select_sem)
>>>>> +    {
>>>>> +      char name[MAX_PATH];
>>>>> +      __small_sprintf(name, "semaphore-%W", get_pipe_name ()->Buffer);
>>>>> +      select_sem = CreateSemaphore (&sec_none, 0, INT32_MAX, name);
>>>>> +    }
>>>>>     return 1;
>>>>>   err_close_reader:
>>>>>     saved_errno = get_errno ();
>>>>
>>>> Should this be:
>>>>> +      select_sem = CreateSemaphore (sa_buf, 0, INT32_MAX, name);
>>>> ?
>>>
>>> I revised the patch a bit.
>>
>> Sorry, I revised the patch again.
> 
> Thanks!  This is an amazing speed-up.  Here's what I see on my system:
> 
> Using the HEAD of topic/pipe:
> 
> $ ./fifo_test 0
> 
> Total: 100MB in 7.646128 second, 13.078515MB/s
> 
> $ ./fifo_test 1
> 
> Total: 100MB in 5.472798 second, 18.272189MB/s
> 
> $ ./fifo_test 2
> 
> Total: 100MB in 0.191965 second, 520.928837MB/s
> 
> $ ./fifo_test 3
> wwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrr 
> 
> Total: 100MB in 0.025944 second, 3854.440894MB/s
> 
> After applying your patch:
> 
> $ ./fifo_test 0
> 
> Total: 100MB in 0.074328 second, 1345.391630MB/s
> 
> $ ./fifo_test 1
> 
> Total: 100MB in 0.062126 second, 1609.632038MB/s
> 
> $ ./fifo_test 2
> 
> Total: 100MB in 0.013286 second, 7527.003124MB/s
> 
> $ ./fifo_test 3
> wwwwrrrrrrrrrr
> Total: 100MB in 0.014044 second, 7120.326396MB/s
> 
> I need to study your patch a little more, but then I'll push it if I don't see 
> any problems.
> 
> Thanks again.  This is great.
> 
> Ken
> 
> P.S. I wrote this yesterday before you sent further revisions, but I forgot to 
> send it.  I'll recheck the latest version shortly.

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.

Ken