From: Eric Whitney Subject: Re: [RFC, PATCH] Avoid hot statistics cache line in ext4 extent cache Date: Fri, 13 Apr 2012 15:01:47 -0400 Message-ID: <4F88781B.9090005@hp.com> References: <4F70F51F.8030405@linux.intel.com> <20120326235707.GC19489@thunk.org> <1334339612.3796.2.camel@schen9-DESK> <1334341876.3796.8.camel@schen9-DESK> <20120413183722.GG26332@thunk.org> <20120413184158.GZ17822@one.firstfloor.org> <20120413184823.GA5898@thunk.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Andi Kleen , Tim Chen , Linus Torvalds , Vivek Haldar , Andreas Dilger , linux-ext4@vger.kernel.org To: Ted Ts'o Return-path: Received: from g1t0027.austin.hp.com ([15.216.28.34]:34576 "EHLO g1t0027.austin.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756144Ab2DMTBx (ORCPT ); Fri, 13 Apr 2012 15:01:53 -0400 In-Reply-To: <20120413184823.GA5898@thunk.org> Sender: linux-ext4-owner@vger.kernel.org List-ID: On 04/13/2012 02:48 PM, Ted Ts'o wrote: > On Fri, Apr 13, 2012 at 08:41:58PM +0200, Andi Kleen wrote: >>> The reason why I ask this is we're seeing anything like this with Eric >>> Whitney's 48 CPU scalability testing; we're not CPU bottlenecked, and >>> I don't even see evidence of a larger than usual CPU utilization >>> compared to other file systems. >> >> I bet Eric didn't test with this statistic counter. > > Huh? You can't turn it off, and he's been doing regular scalability > tests at least once per kernel release. Yes, as recently as 3.4-rc1. I saw Andi's patch, and tested it this week against that baseline with the ffsb profiles we've been using for ext4 (and other filesystem) scalability measurements. I didn't get a noticeable delta for throughput or reported CPU utilization on my 48 core eight node NUMA test setup. That said, I plan to look at this more closely to verify that my workloads should have seen a delta in the first place. Ted knows them well, though. It's worth noting that I've got plenty of free CPU capacity while running the workload, which differs from Andi's/Tim's description. > > Can you say a bit more about exactly how you are doing this test and > what are the "other issues" where this is becoming a bottleneck? If > possible I'd like to ask Eric if he can add it to his regular > scalability tests. Yes, I'm certainly willing to do that if practical, and I'm curious to know more about what the workload looks like. Eric > > Thanks, > > - Ted > -- > To unsubscribe from this list: send the line "unsubscribe linux-ext4" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html