From mboxrd@z Thu Jan 1 00:00:00 1970 From: Chris Mason Subject: Re: Btrfs v0.16 released Date: Thu, 14 Aug 2008 21:25:54 -0400 Message-ID: <1218763554.15342.460.camel@think.oraclecorp.com> 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> Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Cc: Peter Zijlstra , linux-btrfs , linux-kernel , linux-fsdevel To: Andi Kleen Return-path: In-Reply-To: <20080814211756.GC13814@one.firstfloor.org> Sender: linux-btrfs-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org On Thu, 2008-08-14 at 23:17 +0200, Andi Kleen wrote: > On Thu, Aug 14, 2008 at 05:00:56PM -0400, Chris Mason wrote: > > Btrfs defaults 57.41 MB/s Looks like I can get the btrfs defaults up to 64MB/s with some writeback tweaks. > > Btrfs dup no csum 74.59 MB/s > > With duplications checksums seem to be quite costly (CPU bound?) > 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? 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. -chris