From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andi Kleen <andi@firstfloor.org>
Subject: Re: Btrfs v0.16 released
Date: Fri, 15 Aug 2008 03:39:34 +0200
Message-ID: <20080815013934.GE19125@one.firstfloor.org>
References: <1217962876.15342.33.camel@think.oraclecorp.com> <1218100464.8625.9.camel@twins> <1218105597.15342.189.camel@think.oraclecorp.com> <877ias66v4.fsf@basil.nowhere.org> <1218221293.15342.263.camel@think.oraclecorp.com> <1218747656.15342.439.camel@think.oraclecorp.com> <20080814211756.GC13814@one.firstfloor.org> <1218763554.15342.460.camel@think.oraclecorp.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Cc: Andi Kleen <andi@firstfloor.org>,
	Peter Zijlstra <peterz@infradead.org>,
	linux-btrfs <linux-btrfs@vger.kernel.org>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>
To: Chris Mason <chris.mason@oracle.com>
Return-path: <linux-fsdevel-owner@vger.kernel.org>
In-Reply-To: <1218763554.15342.460.camel@think.oraclecorp.com>
List-ID: <linux-btrfs.vger.kernel.org>

> The async worker threads should be spreading the load across CPUs pretty
> well, and even a single CPU could keep up with 100MB/s checksumming.
> But, the async worker threads do randomize the IO somewhat because the
> IO goes from pdflush -> one worker thread per CPU -> submit_bio.  So,
> maybe that 3rd thread is more than the drive can handle?

You have more threads with duplication? 

> 
> btrfsck tells me the total size of the btree is only 20MB larger with
> checksumming on.
> 
> > > Btrfs no duplication            76.83 MB/s
> > > Btrfs no dup no csum no inline  76.85 MB/s
> > 
> > But without duplication they are basically free here at least
> > in IO rate. Seems odd?
> > 
> > Does it compute them twice in the duplication case perhaps?
> > 
> 
> The duplication happens lower down in the stack, they only get done
> once.

Ok was just speculation. The big difference still seems odd.

-Andi