Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753798AbZGAMxY (ORCPT ); Wed, 1 Jul 2009 08:53:24 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751678AbZGAMxR (ORCPT ); Wed, 1 Jul 2009 08:53:17 -0400 Received: from ns.dcl.info.waseda.ac.jp ([133.9.216.194]:64859 "EHLO ns.dcl.info.waseda.ac.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751053AbZGAMxQ (ORCPT ); Wed, 1 Jul 2009 08:53:16 -0400 Date: Wed, 01 Jul 2009 21:53:04 +0900 (JST) Message-Id: <20090701.215304.864843820974206197.mitake@dcl.info.waseda.ac.jp> To: mingo@elte.hu Cc: acme@redhat.com, a.p.zijlstra@chello.nl, andi@firstfloor.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH][RFC] Adding information of counts processes acquired how many spinlocks to schedstat From: Hitoshi Mitake In-Reply-To: <20090701110620.GB15958@elte.hu> References: <20090701090749.GA13535@elte.hu> <20090701.184232.131509470674490734.mitake@dcl.info.waseda.ac.jp> <20090701110620.GB15958@elte.hu> X-Mailer: Mew version 5.2 on Emacs 22.2 / Mule 5.0 (SAKAKI) Mime-Version: 1.0 Content-Type: Text/Plain; charset=utf-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from base64 to 8bit by alpha.home.local id n61CrUoU026898 Content-Length: 3939 Lines: 89 From: Ingo Molnar Subject: Re: [PATCH][RFC] Adding information of counts processes acquired how many spinlocks to schedstat Date: Wed, 1 Jul 2009 13:06:20 +0200 > > * Hitoshi Mitake wrote: > > > From: Ingo Molnar > > Subject: Re: [PATCH][RFC] Adding information of counts processes acquired how many spinlocks to schedstat > > Date: Wed, 1 Jul 2009 11:07:49 +0200 > > > > > > > > * Hitoshi Mitake wrote: > > > > > > > From: Andi Kleen > > > > Subject: Re: [PATCH][RFC] Adding information of counts processes acquired how many spinlocks to schedstat > > > > Date: Wed, 01 Jul 2009 09:38:04 +0200 > > > > > > > > > Hitoshi Mitake writes: > > > > > > > > > > > Hi, > > > > > > > > > > > > I wrote a test patch which add information of counts processes acquired how many spinlocks to schedstat. > > > > > > After applied this patch, /proc//sched will change like this, > > > > > > > > > > The problem is that spinlocks are very common and schedstats is > > > > > enabled commonly in production kernels. You would need to > > > > > demonstrate that such a change doesn't have significant > > > > > performance impact. For me it looks like it has. > > > > > > > > I agree with your opinion about performance impact. > > > > I thought this will make no problem, > > > > because schedstat is categorized as "Kernel hacking" section. > > > > But according to you, many production kernels enable it > > > > so my patch will make widespread performance degradation. > > > > I didn't know that, sorry. > > > > > > His arguments are bogus: both lockstat and perfcounters are optional > > > (and default off), and the sw counter can be made near zero cost > > > even if both perfcounters and lockstat is enabled. Also, sw counters > > > are generally per CPU, etc. so not a performance issue. > > > > > > The only (small) overhead will be when the lock-acquire sw counter > > > is actively enabled because you run 'perf stat -e lock-acquire' - > > > but that is expected and inherent in pretty much any kind of > > > instrumentation. > > > > > > The feature you are working on has the chance to be a very useful > > > and popular piece of instrumentation. Being able to tell the lock > > > acquire stats on a per task, per workload, per CPU or system-wide > > > basis is a unique capability no other tool can offer right now. > > > > > > Andi is often trolling perfcounters related (and other) threads, > > > please dont let yourself be deterred by that and feel free to ignore > > > him. > > OK, at least it is truth that > > counter in perfcounters makes only valid overhead. > > > > And I have a question, > > I tried to build perf, but I got a build error, > > > > util/symbol.c: In function ‘dso__load_sym’: > > util/symbol.c:466: error: ‘ELF_C_READ_MMAP’ undeclared (first use in this function) > > util/symbol.c:466: error: (Each undeclared identifier is reported only once > > util/symbol.c:466: error: for each function it appears in.) > > > > I used this libelf, > > http://www.mr511.de/software/english.html > > but constant ELF_C_READ_MMAP is not provided... > > > > which "libelf" should I use? > > It seems that there are some libelf implementations. > > I use the elfutils-libelf* packages: > > elfutils-libelf-devel-static-0.141-1.fc10.i386 > elfutils-0.141-1.fc10.i386 > elfutils-libelf-0.141-1.fc10.i386 > elfutils-libs-0.141-1.fc10.i386 > elfutils-libelf-devel-0.141-1.fc10.i386 > > do they work fine or you? I'm a Debian user, so I build this library from source https://fedorahosted.org/releases/e/l/elfutils/elfutils-0.141.tar.bz2 And I succeed to build perf, thanks! ????{.n?+???????+%?????ݶ??w??{.n?+????{??G?????{ay?ʇڙ?,j??f???h?????????z_??(?階?ݢj"???m??????G????????????&???~???iO???z??v?^?m???? ????????I?