From owner-freebsd-fs@FreeBSD.ORG  Thu Apr 11 17:08:56 2013
Return-Path: <owner-freebsd-fs@FreeBSD.ORG>
Delivered-To: freebsd-fs@freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org
 [IPv6:2001:1900:2254:206a::19:1])
 by hub.freebsd.org (Postfix) with ESMTP id 5D81EFC
 for <freebsd-fs@freebsd.org>; Thu, 11 Apr 2013 17:08:56 +0000 (UTC)
 (envelope-from nowakpl@platinum.linux.pl)
Received: from platinum.linux.pl (platinum.edu.pl [81.161.192.4])
 by mx1.freebsd.org (Postfix) with ESMTP id 239A4AE3
 for <freebsd-fs@freebsd.org>; Thu, 11 Apr 2013 17:08:55 +0000 (UTC)
Received: by platinum.linux.pl (Postfix, from userid 87)
 id CAB4647E29; Thu, 11 Apr 2013 19:08:54 +0200 (CEST)
X-Spam-Checker-Version: SpamAssassin 3.3.2 (2011-06-06) on platinum.linux.pl
X-Spam-Level: 
X-Spam-Status: No, score=-1.3 required=3.0 tests=ALL_TRUSTED,AWL
 autolearn=disabled version=3.3.2
Received: from [10.255.1.2] (unknown [83.151.38.73])
 by platinum.linux.pl (Postfix) with ESMTPA id 9DEB047E24
 for <freebsd-fs@freebsd.org>; Thu, 11 Apr 2013 19:08:54 +0200 (CEST)
Message-ID: <5166EE14.1090806@platinum.linux.pl>
Date: Thu, 11 Apr 2013 19:08:36 +0200
From: Adam Nowacki <nowakpl@platinum.linux.pl>
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64;
 rv:17.0) Gecko/20130328 Thunderbird/17.0.5
MIME-Version: 1.0
To: freebsd-fs@freebsd.org
Subject: Re: ZFS slow reads for unallocated blocks
References: <5166EA43.7050700@platinum.linux.pl> <5166ECBA.1090005@gmail.com>
In-Reply-To: <5166ECBA.1090005@gmail.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
X-BeenThere: freebsd-fs@freebsd.org
X-Mailman-Version: 2.1.14
Precedence: list
List-Id: Filesystems <freebsd-fs.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/options/freebsd-fs>,
 <mailto:freebsd-fs-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-fs>
List-Post: <mailto:freebsd-fs@freebsd.org>
List-Help: <mailto:freebsd-fs-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-fs>,
 <mailto:freebsd-fs-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Thu, 11 Apr 2013 17:08:56 -0000

On 2013-04-11 19:02, Chuck Burns wrote:
> On 4/11/2013 11:52 AM, Adam Nowacki wrote:
>> This one is quite weird - reads from files that were created and resized
>> with ftruncate (so no actual data on disk) are considerably slower and
>> use more CPU time than files with data. If compression is enabled this
>> will also affect files with long runs of zeroes as ZFS won't write any
>> data to disk in this case. There is no I/O on the pool during the read
>> tests - all fits into 10GB ARC.
>>
>> FreeBSD storage 9.1-RELEASE FreeBSD 9.1-RELEASE #0: Sat Feb 23 15:51:26
>> UTC 2013     root@storage:/usr/obj/usr/src/sys/GENERIC  amd64
> <snip>
>
> Sounds like it could be a CPU bottleneck? How about some cpu info?
>
>

hw.model: AMD FX(tm)-4100 Quad-Core Processor
hw.ncpu: 4

But this doesn't matter much as CPU time should be compared relative to 
other tests - 1 second versus 15 seconds on the same CPU.