From: Eric Whitney Subject: Re: [PATCH] ext4: Use single thread to perform DIO unwritten convertion Date: Mon, 07 Mar 2011 10:47:25 -0500 Message-ID: <4D74FE0D.4090207@hp.com> References: <1299180594.2826.6.camel@mingming-laptop> <20110305174639.GD11120@thunk.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Mingming Cao , linux-ext4@vger.kernel.org To: Ted Ts'o Return-path: Received: from g1t0029.austin.hp.com ([15.216.28.36]:16473 "EHLO g1t0029.austin.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754168Ab1CGPrW (ORCPT ); Mon, 7 Mar 2011 10:47:22 -0500 In-Reply-To: <20110305174639.GD11120@thunk.org> Sender: linux-ext4-owner@vger.kernel.org List-ID: On 03/05/2011 12:46 PM, Ted Ts'o wrote: > On Thu, Mar 03, 2011 at 11:29:54AM -0800, Mingming Cao wrote: >> While running ext4 testing on multiple core, we found there are per >> cpu ext4-dio-unwritten threads processing conversion from unwritten >> extents to written for IOs completed from async direct IO patch. >> Per filesystem is enough, we don't need per cpu threads to work on >> conversion. >> >> Signed-off-by: Mingming Cao > > Eric, would you be able to do a very quick sanity check on your > 48-core machine? I can definitely see how having a huge number of > threads per file system could be problematic, especially on a system > with 32 or 64 ext4 file systems. I'm curious though if we'll end up > taking a performance hit on direct I/O workloads. > Hi Ted: Sure, I can do that - I'll queue it up once I'm done with the "for .39" patch measurements. > If I remember correctly we currently have large file create with DIO > turned off, right? Would it be possible to do a large file create > with DIO enabled, and do a quick run both with and without this patch? That's right, we're not measuring DIO right now. I think I've got enough hardware to run a filesystem per core (or more), and I think it should be straightforward to write a modified ffsb profile to run (say) 48 filesystems in parallel. > > In the future it would also be interesting to see how we are doing > versus other file systems using a DIO workload. This is a probably > another area where I suspect some lockstat and oprofile runs may give > us opportunities for further optimization. Yes - as discussed at Plumber's. I'll put that on the list as well. With luck, there should be some time towards the end of the .39 merge window. Eric > > - Ted