From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 8363 invoked by alias); 20 Apr 2011 20:57:51 -0000 Received: (qmail 8355 invoked by uid 22791); 20 Apr 2011 20:57:51 -0000 X-SWARE-Spam-Status: No, hits=-6.1 required=5.0 tests=AWL,BAYES_00,RCVD_IN_DNSWL_HI,SPF_HELO_PASS,T_RP_MATCHES_RCVD X-Spam-Check-By: sourceware.org Received: from mx1.redhat.com (HELO mx1.redhat.com) (209.132.183.28) by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Wed, 20 Apr 2011 20:57:37 +0000 Received: from int-mx10.intmail.prod.int.phx2.redhat.com (int-mx10.intmail.prod.int.phx2.redhat.com [10.5.11.23]) by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id p3KKvZxu004700 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK); Wed, 20 Apr 2011 16:57:35 -0400 Received: from [10.3.113.81] (ovpn-113-81.phx2.redhat.com [10.3.113.81]) by int-mx10.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id p3KKvYBN016088; Wed, 20 Apr 2011 16:57:34 -0400 Message-ID: <4DAF48BE.9020904@redhat.com> Date: Wed, 20 Apr 2011 20:57:00 -0000 From: Josh Stone User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.15) Gecko/20110307 Fedora/3.1.9-0.39.b3pre.fc14 Lightning/1.0b3pre Thunderbird/3.1.9 MIME-Version: 1.0 To: Jake Maul CC: William Cohen , systemtap@sourceware.org Subject: Re: Linux VFS cache hit rate script References: <4DAF3D59.7020609@redhat.com> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-IsSubscribed: yes Mailing-List: contact systemtap-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Post: List-Help: , Sender: systemtap-owner@sourceware.org X-SW-Source: 2011-q2/txt/msg00132.txt.bz2 On 04/20/2011 01:45 PM, Jake Maul wrote: > On Wed, Apr 20, 2011 at 1:08 PM, William Cohen wrote: >> Why the need for -DMAXMAPENTRIES=100000 on the second example on >> the wiki page? There doesn't seem to be any arrays in the script. > > For some reason on that particular server, I get this error sometimes: > > ERROR: Array overflow, check MAXMAPENTRIES near identifier '$file' at > /usr/share/systemtap/tapset/vfs.stp:769:9 The error location looks bogus, which we should investigate, but this is probably from the array used in vfs.stp:__find_bdevname(). I'm not sure how you could be encountering so many unique "dev" though. >> The following line sounds unsure, need to check that that is really the case: >> >> if (devname=="N/A") { /* N/A means cache hit... right? */ >> >> It would be good to have a better explanation for the "N/A" check. > > This is from the beginner's guide, actually: > > http://docs.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/6/html/SystemTap_Beginners_Guide/mainsect-disk.html > > It bothers me too, because I can't find any documentation that says > explicitly when you would get an 'N/A' devname. I don't know if it's a > SystemTap thing or a kernel thing, but being that I don't have > experience working on either, I'm fairly lost. That string comes from dev.stp:bdevname(bdev), whenever the parameter is zero. I'm not sure about the particulars though, whether bdev==0 really means it's a cache hit... Josh