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xen-devel
Re: [Xen-devel] blktap2 device creation failing after 162 devices w/Xen4
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 <keir.fraser@xxxxxxxxxx>
>> 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@xxxxxxxxxxxxxxxxxxx
>> http://lists.xensource.com/xen-devel
>>
>
>
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@xxxxxxxxxxxxxxxxxxx
> http://lists.xensource.com/xen-devel
>
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