From mboxrd@z Thu Jan 1 00:00:00 1970 From: John McCullough Subject: Re: blktap2 device creation failing after 162 devices w/Xen4.0 + linux-2.6.31.13 Date: Tue, 13 Apr 2010 22:40:01 -0700 Message-ID: <4BC55531.7080005@cs.ucsd.edu> References: <4BC50A5A.1020501@cs.ucsd.edu> <1271216280.25413.1782.camel@agari.van.xensource.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1271216280.25413.1782.camel@agari.van.xensource.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Daniel Stodden Cc: Ian Pratt , "xen-devel@lists.xensource.com" List-Id: xen-devel@lists.xenproject.org Daniel, That did the trick and got us up to 256, Thanks! Out of curiosity, what's standing in the way of more devices? We tried raising the MAX_*_DEVICES constants in these files to 512, but didn't have any luck: linux-2.6-pvops.git/drivers/xen/blktap/blktap.h tools/blktap2/include/blktaplib.h tools/blktap/lib/blktaplib.h (The error is now "vbd open failed: -6") I noticed an artificial limit of 26*26 in the tapdev naming scheme, but I didn't look very thoroughly. Thanks again, John Daniel Stodden wrote: > Hi. > > Please echo $((N * (32 * 11 + 50) + SOME_HEADROOM)) > to /proc/sys/fs/aio-max-nr. Or set it up in sysctl.conf. > > Where N is the number of devices you desire. > > As for the apparently missing big fat complaint you should have seen pop > in syslog, I'll keep it in mind for the next update. :} > > Cheers, > Daniel > > On Tue, 2010-04-13 at 20:20 -0400, John McCullough wrote: > >> I have been working with a colleague to get a large number of small VMs >> running on a single system. We were hoping for at least 100, but we >> seem to be topping out around 81. Each VM has a disk image and a swap >> image. It seemed like we were hitting a blktap limit, so we tried >> bumping up the MAX macros in tool/blktap2 and the linux driver, with no >> change. (Though we haven't hit the theoretical 256 blktap devices yet). >> >> (Initially we were only able to get 64 VMs until we bumped >> CONFIG_NR_CPUS from 8 to 64 to increase the number of dynirqs). >> >> To isolate the problem, I tried creating a large number of blktap >> devices in the dom0 with no guests running and I ran into the same >> ceiling (162 total devices). Commands to reproduce the problem follow: >> >> echo 9 > /sys/class/blktap2/verbosity >> >> for x in `seq 0 163`; do >> if ( ! dd if=/dev/zero of=/scratch/test-$x.img bs=1 count=1 >> seek=1M 2> /dev/null); then >> echo "Qemu fail on $x"; exit 1 >> fi >> if ( ! tapdisk2 -n aio:/scratch/test-$x.img) ; then >> echo "blktap fail on $x"; exit 1 >> fi >> done >> >> The result: >> ... >> /dev/xen/blktap-2/tapdev159 >> /dev/xen/blktap-2/tapdev160 >> /dev/xen/blktap-2/tapdev161 >> /dev/xen/blktap-2/tapdev162 >> unrecognized child response >> blktap fail on 163 >> >> Dmesg output associated with 163: >> [ 1288.839978] blktap_sysfs_create: adding attributes for dev >> ffff88019e4d1e00 >> [ 1288.840947] blktap_sysfs_destroy >> >> (Output for the prior devices includes processing a request, and a >> blktap_device_finish_request) >> >> No related xm dmesg output. >> >> $ hg tip >> changeset: 21091:f28f1ee587c8 >> tag: tip >> user: Keir Fraser >> date: Wed Apr 07 12:38:28 2010 +0100 >> summary: Added signature for changeset 484179b2be5d >> >> $ uname -a >> Linux sysnet121 2.6.32-3-amd64 #1 SMP Wed Feb 24 18:07:42 UTC 2010 >> x86_64 GNU/Linux >> >> Has anyone had contrary experience? Does anyone know where the 162 max >> is coming from? >> >> Thanks, >> John >> >> _______________________________________________ >> Xen-devel mailing list >> Xen-devel@lists.xensource.com >> http://lists.xensource.com/xen-devel >> > > > > _______________________________________________ > Xen-devel mailing list > Xen-devel@lists.xensource.com > http://lists.xensource.com/xen-devel >