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Date:	Sat, 26 Jun 2004 11:45:04 -0400
From:	"Pierre A. Humblet" <pierre DOT humblet AT ieee DOT org>
To:	cygwin AT cygwin DOT com
Subject:	Re: higher-level IO very slow with cygwin1.dll 5.10 (due to set_flags?)
Message-ID:	<20040626154504.GA961349@hpn5170x>
Mail-Followup-To:	"Pierre A. Humblet" <pierre DOT humblet AT ieee DOT org>, cygwin AT cygwin DOT com
References:	<opr96vbqwilh6y6a AT localhost>
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On Sat, Jun 26, 2004 at 02:36:52AM -0400, Joseph wrote:
> Thanks to those who responded to my post.
> 
> I am not sure though if all of you read the
> entire sequence of the thread.
> 
> In my first post, I did attach an excerpt
> from an strace dump of a sample program that
> seemed to show "where the time is going".

You initial accusation against set_flags was unfounded
and led nowhere. But you have a very good point.

Your "fast" program is doing reads in blocks of 1024.
Your "slow" program is using getc.

I observed that the slow program was 20 times slower
than the fast one, even though strace showed that getc
was properly calling read in blocks of 1024.

I then noticed that getc is not implemented as a macro
on Cygwin. It's a newlib function
 
74      int
75      _DEFUN(getc, (fp),
76             register FILE *fp)
77      {
78        int result;
79        _flockfile (fp);
80        /* CHECK_INIT is called (eventually) by __srefill.  */
81        result = __sgetc (fp);
82        _funlockfile (fp);
83        return result;
(gdb) 
84      }

_flockfile calls a bunch of pthread functions. That's where all
the time is spent, a large part of it verifying that pointers
are valid.

It's probably a relatively new feature of Cygwin. Others may know
more about the history and justification of implementation.

Pierre

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