Mailing-List: contact cygwin-help AT cygwin DOT com; run by ezmlm
List-Subscribe: <mailto:cygwin-subscribe AT cygwin DOT com>
List-Archive: <http://sourceware.org/ml/cygwin/>
List-Post: <mailto:cygwin AT cygwin DOT com>
List-Help: <mailto:cygwin-help AT cygwin DOT com>, <http://sourceware.org/ml/#faqs>
Sender: cygwin-owner AT cygwin DOT com
Mail-Followup-To: cygwin AT cygwin DOT com
Delivered-To: mailing list cygwin AT cygwin DOT com
Date: Mon, 26 Jul 2004 10:30:46 +0200
From: Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
To: cygwin AT cygwin DOT com
Subject: Re: Setting SHMMAX in Cygwin
Message-ID: <20040726083046.GA732@cygbert.vinschen.de>
Reply-To: cygwin AT cygwin DOT com
Mail-Followup-To: cygwin AT cygwin DOT com
References: <001a01c47281$c8b02070$99280518 AT Gene>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <001a01c47281$c8b02070$99280518@Gene>
User-Agent: Mutt/1.4.2i

On Jul 25 12:58, Gene C. Ruzicka wrote:
> A code I'm porting to Cygwin requires tuning the
> size of the shareable memory segment to obtain
> optimal performance.  I am using cygserver to
> access IPC utilities.  
> 
> cygserver.conf doesn't allow one to set the maximum shareable 
> segment size, SHMMAX directly.  Instead, it seems SHMMAX
> is set in this code fragment in function shminit in cygserver:
> 
>  int i;
>  TUNABLE_INT_FETCH("kern.ipc.shmmaxpgs", &shminfo.shmall);
>  for (i = PAGE_SIZE; i > 0; i--) {
>   shminfo.shmmax = shminfo.shmall * PAGE_SIZE;
>   if (shminfo.shmmax >= shminfo.shmall)
>    break;
>  }
> 
> Thus, SHMMAX = SHMMAXPGS*PAGE_SIZE , in which
> SHMMAXPGS is configurable in cygserver.conf, and PAGE_SIZE
> is the system's page size.  So, this suggests that if you have to set
> SHMMAXPGS in order to set SHMMAX. Is this correct?

Yes.

> Further comment: Uncovering this information was somewhat painful.

Didn't you read /usr/share/doc/Cygwin/cygserver.README and in turn
/etc/cygserver.conf in the first place?  The configuration file contains
the comment

  "kern.ipc.shmmaxpgs: Maximum pages available for XSI shared memory."

I thought that explains it.


Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Co-Project Leader          mailto:cygwin AT cygwin DOT com
Red Hat, Inc.

--
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/