From owner-freebsd-geom@FreeBSD.ORG  Fri Dec 10 14:48:27 2010
Return-Path: <owner-freebsd-geom@FreeBSD.ORG>
Delivered-To: freebsd-geom@freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34])
	by hub.freebsd.org (Postfix) with ESMTP id 5AFE31065672;
	Fri, 10 Dec 2010 14:48:27 +0000 (UTC) (envelope-from avg@freebsd.org)
Received: from citadel.icyb.net.ua (citadel.icyb.net.ua [212.40.38.140])
	by mx1.freebsd.org (Postfix) with ESMTP id 728E78FC15;
	Fri, 10 Dec 2010 14:48:26 +0000 (UTC)
Received: from odyssey.starpoint.kiev.ua (alpha-e.starpoint.kiev.ua
	[212.40.38.101])
	by citadel.icyb.net.ua (8.8.8p3/ICyb-2.3exp) with ESMTP id QAA09006;
	Fri, 10 Dec 2010 16:48:24 +0200 (EET) (envelope-from avg@freebsd.org)
Message-ID: <4D023DB7.9080509@freebsd.org>
Date: Fri, 10 Dec 2010 16:48:23 +0200
From: Andriy Gapon <avg@freebsd.org>
User-Agent: Mozilla/5.0 (X11; U; FreeBSD amd64; en-US;
	rv:1.9.2.12) Gecko/20101029 Lightning/1.0b2 Thunderbird/3.1.6
MIME-Version: 1.0
To: Lev Serebryakov <lev@serebryakov.spb.ru>
References: <1365605559.20101210162253@serebryakov.spb.ru>
In-Reply-To: <1365605559.20101210162253@serebryakov.spb.ru>
X-Enigmail-Version: 1.1.2
Content-Type: text/plain; charset=windows-1251
Content-Transfer-Encoding: 7bit
Cc: freebsd-hackers@freebsd.org, freebsd-geom@freebsd.org
Subject: Re: Where userland read/write requests, whcih is larger than MAXPHYS,
 are splitted?
X-BeenThere: freebsd-geom@freebsd.org
X-Mailman-Version: 2.1.5
Precedence: list
List-Id: GEOM-specific discussions and implementations
	<freebsd-geom.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-geom>,
	<mailto:freebsd-geom-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-geom>
List-Post: <mailto:freebsd-geom@freebsd.org>
List-Help: <mailto:freebsd-geom-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-geom>,
	<mailto:freebsd-geom-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Fri, 10 Dec 2010 14:48:27 -0000

on 10/12/2010 15:22 Lev Serebryakov said the following:
> Hello, Freebsd-geom.
> 
>    I'm  digging  thought  GEOM/IO  code  and  can not find place, where
>  requests  from  userland to read more than MAXPHYS bytes, is splitted
>  into  several "struct bio"?

Check out g_disk_start().
The split is done based on disk-specific d_maxsize, not hardcoded MAXPHYS, of course.

>       It seems, that these children request are issued one-by-one, not in
>  parallel,   am  I  right?  Why?  It  breaks  down  parallelism,  when
>  underlying GEOM can process several requests simoltaneously?

How do you *issue* the child requests in parallel?
Of course, they can *run* in parallel if system configuration permits that and
request run time is sufficient for an overlap to happen.
Besides, there are no geoms under disk geom, it works on peripheral drivers.

But maybe I misunderstood your question and you talked about a different I/O layer
or different I/O path.

-- 
Andriy Gapon