From owner-freebsd-current@freebsd.org  Tue Apr  5 06:10:18 2016
Return-Path: <owner-freebsd-current@freebsd.org>
Delivered-To: freebsd-current@mailman.ysv.freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org
 [IPv6:2001:1900:2254:206a::19:1])
 by mailman.ysv.freebsd.org (Postfix) with ESMTP id E0520B01939
 for <freebsd-current@mailman.ysv.freebsd.org>;
 Tue,  5 Apr 2016 06:10:18 +0000 (UTC)
 (envelope-from kostikbel@gmail.com)
Received: from kib.kiev.ua (kib.kiev.ua [IPv6:2001:470:d5e7:1::1])
 (using TLSv1 with cipher DHE-RSA-CAMELLIA256-SHA (256/256 bits))
 (Client did not present a certificate)
 by mx1.freebsd.org (Postfix) with ESMTPS id 78D5714CB;
 Tue,  5 Apr 2016 06:10:18 +0000 (UTC)
 (envelope-from kostikbel@gmail.com)
Received: from tom.home (kostik@localhost [127.0.0.1])
 by kib.kiev.ua (8.15.2/8.15.2) with ESMTPS id u356ADHJ070848
 (version=TLSv1 cipher=DHE-RSA-CAMELLIA256-SHA bits=256 verify=NO);
 Tue, 5 Apr 2016 09:10:13 +0300 (EEST)
 (envelope-from kostikbel@gmail.com)
DKIM-Filter: OpenDKIM Filter v2.10.3 kib.kiev.ua u356ADHJ070848
Received: (from kostik@localhost)
 by tom.home (8.15.2/8.15.2/Submit) id u356ADbl070846;
 Tue, 5 Apr 2016 09:10:13 +0300 (EEST)
 (envelope-from kostikbel@gmail.com)
X-Authentication-Warning: tom.home: kostik set sender to kostikbel@gmail.com
 using -f
Date: Tue, 5 Apr 2016 09:10:13 +0300
From: Konstantin Belousov <kostikbel@gmail.com>
To: John Baldwin <jhb@freebsd.org>
Cc: Ryan Stone <rysto32@gmail.com>,
 FreeBSD Current <freebsd-current@freebsd.org>
Subject: Re: accessing a PCIe register from userspace through kmem or other
 ways ?
Message-ID: <20160405061013.GE1741@kib.kiev.ua>
References: <CA+hQ2+iU4odjhaNicFA4QjvSZR2OZOOy+Fu4LTqsibdoK4M8zg@mail.gmail.com>
 <9376230.YZMFsgSvTf@ralph.baldwin.cx>
 <CAFMmRNzpOgBPsBezOyUZ_=qjCywfADx8MuJWdaWb_D+7UCmi7Q@mail.gmail.com>
 <5009932.qXoZ6E4rhX@ralph.baldwin.cx>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <5009932.qXoZ6E4rhX@ralph.baldwin.cx>
User-Agent: Mutt/1.5.24 (2015-08-30)
X-Spam-Status: No, score=-2.0 required=5.0 tests=ALL_TRUSTED,BAYES_00,
 DKIM_ADSP_CUSTOM_MED,FREEMAIL_FROM,NML_ADSP_CUSTOM_MED autolearn=no
 autolearn_force=no version=3.4.1
X-Spam-Checker-Version: SpamAssassin 3.4.1 (2015-04-28) on tom.home
X-BeenThere: freebsd-current@freebsd.org
X-Mailman-Version: 2.1.21
Precedence: list
List-Id: Discussions about the use of FreeBSD-current
 <freebsd-current.freebsd.org>
List-Unsubscribe: <https://lists.freebsd.org/mailman/options/freebsd-current>, 
 <mailto:freebsd-current-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-current/>
List-Post: <mailto:freebsd-current@freebsd.org>
List-Help: <mailto:freebsd-current-request@freebsd.org?subject=help>
List-Subscribe: <https://lists.freebsd.org/mailman/listinfo/freebsd-current>, 
 <mailto:freebsd-current-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Tue, 05 Apr 2016 06:10:19 -0000

On Mon, Apr 04, 2016 at 09:02:49PM -0700, John Baldwin wrote:
> kib@ fixed /dev/mem to handle addresses beyond the direct map limit to use
> temporary mappings instead of failing with EFAULT in 277051 which was only
> committed to HEAD last January, so well after 8.2.

The mmap(2) interface to /dev/mem did not have the issue ever.  The problem
was only with the read(2)/write(2) accesses.

>From what I understand, since the goal of the OP was to measure BAR
access latencies, read(2) (or write) is unsuitable for him for obvious
reasons.