Mailing-List: contact cygwin-help@cygwin.com; run by ezmlm List-Subscribe: List-Archive: List-Post: List-Help: , Sender: cygwin-owner@cygwin.com Mail-Followup-To: cygwin@cygwin.com Delivered-To: mailing list cygwin@cygwin.com Date: Sat, 26 Jun 2004 11:45:04 -0400 From: "Pierre A. Humblet" To: cygwin@cygwin.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" , cygwin@cygwin.com References: Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.4.1i 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 -- Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple Problem reports: http://cygwin.com/problems.html Documentation: http://cygwin.com/docs.html FAQ: http://cygwin.com/faq/