From owner-freebsd-current@freebsd.org  Sun Jun  4 07:54:50 2017
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 16EF9AFD127
 for <freebsd-current@mailman.ysv.freebsd.org>;
 Sun,  4 Jun 2017 07:54:50 +0000 (UTC) (envelope-from hps@selasky.org)
Received: from mail.turbocat.net (turbocat.net [88.99.82.50])
 (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits))
 (Client did not present a certificate)
 by mx1.freebsd.org (Postfix) with ESMTPS id D1F396A477
 for <freebsd-current@freebsd.org>; Sun,  4 Jun 2017 07:54:48 +0000 (UTC)
 (envelope-from hps@selasky.org)
Received: from hps2016.home.selasky.org (unknown [62.141.129.119])
 (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits))
 (No client certificate requested)
 by mail.turbocat.net (Postfix) with ESMTPSA id A235D260873;
 Sun,  4 Jun 2017 09:54:39 +0200 (CEST)
Subject: Re: Time to increase MAXPHYS?
To: Tomoaki AOKI <junchoon@dec.sakura.ne.jp>, freebsd-current@freebsd.org
References: <0100015c6fc1167c-6e139920-60d9-4ce3-9f59-15520276aebb-000000@email.amazonses.com>
 <972dbd34-b5b3-c363-721e-c6e48806e2cd@elischer.org>
 <3719c729-9434-3121-cf52-393a4453d0b2@freebsd.org>
 <CANCZdfrkc1ERKnJr4JzHpePmU+rN5JOgAVePCShPHLDCAE19=w@mail.gmail.com>
 <CANCZdfpD3G8gR=C2_AekM6VeJ6dzKOnP820OOoF1M_eS0MfJ3g@mail.gmail.com>
 <20170604163948.eb5f74ce2a233b8f204ba671@dec.sakura.ne.jp>
From: Hans Petter Selasky <hps@selasky.org>
Message-ID: <15e42fd1-055d-28f6-5e24-1448e16954a9@selasky.org>
Date: Sun, 4 Jun 2017 09:52:36 +0200
User-Agent: Mozilla/5.0 (X11; FreeBSD amd64; rv:52.0) Gecko/20100101
 Thunderbird/52.1.1
MIME-Version: 1.0
In-Reply-To: <20170604163948.eb5f74ce2a233b8f204ba671@dec.sakura.ne.jp>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Language: en-US
Content-Transfer-Encoding: 7bit
X-BeenThere: freebsd-current@freebsd.org
X-Mailman-Version: 2.1.23
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: Sun, 04 Jun 2017 07:54:50 -0000

On 06/04/17 09:39, Tomoaki AOKI wrote:
> Hi
> 
> One possibility would be to make it MD build-time OTIONS,
> defaulting 1M on regular systems and 128k on smaller systems.
> 
> Of course I guess making it a tunable (or sysctl) would be best,
> though.
> 

Hi,

A tunable sysctl would be fine, but beware that commonly used firmware 
out there produced in the millions might hang in a non-recoverable way 
if you exceed their "internal limits". Conditionally lowering this 
definition is fine, but increasing it needs to be carefully verified.

For example many USB devices are only tested with OS'es like Windows and 
MacOS and if these have any kind of limitation on the SCSI transfer 
sizes, it is very likely many devices out there do not support any 
larger transfer sizes either.

--HPS