[Scst-devel] [ofa-general] WinOF_2_0_5/SRP initiator: slow reads and eventually hangs

[Chris Worley]

On Tue, Sep 15, 2009 at 10:43 AM, Vladislav Bolkhovitin <vst at vlnb.net> wrote:
> Chris Worley, on 09/15/2009 07:50 PM wrote:
>>
>> On Tue, Sep 15, 2009 at 12:10 AM, Bart Van Assche
>> <bart.vanassche at gmail.com> wrote:
>>>
>>> On Tue, Sep 15, 2009 at 1:03 AM, Chris Worley <worleys at gmail.com> wrote:
>>>>
>>>> On Mon, Sep 14, 2009 at 12:51 PM, Vladislav Bolkhovitin <vst at vlnb.net>
>>>> wrote:
>>>>>
>>>>> Chris Worley, on 09/11/2009 11:50 PM wrote:
>>>>>>
>>>>>> I've definitely removed the switch/firmware from being the cause.
>>>>>>
>>>>>> I'm thinking the reason you can't repeat the test may be latency
>>>>>> related.  We get ~50usecs average latency (on small block sizes),
>>>>>> which can't be achieved using regular SSD's (and rotating drives are
>>>>>> nowhere close).  Maybe a ramdisk would help repeat the issue.
>>>>>
>>>>> I think you should try to reproduce the problem with ramdisk or nullio.
>>>>> By
>>>>> so you will eliminate possible influence of the SSD backend.
>>>>
>>>> W/ 12GB RAM in the target, I created a 7GB ramdisk:
>>>>
>>>> mount -t ramfs -o size=7g ramfs /mnt/
>>>> dd if=/dev/zero of=/mnt/foo bs=1024k count=7000
>>>> echo "open ramdisk /mnt/foo" > /proc/scsi_tgt/vdisk/vdisk
>>>> echo "add ramdisk 2" >/proc/scsi_tgt/groups/Default/devices
>>>>
>>>> Then, on the initiator, I tested it... and it hung during sequential
>>>> 8KB block reads:
>>>>
>>>> fio --rw=read --bs=8k --numjobs=64 --iodepth=64 --sync=0 --direct=1
>>>> --randrepeat=0 \
>>>>  --group_reporting --ioengine=libaio --filename=/dev/sde --name=test
>>>> --loops=10000 --runtime=600
>>>>
>>>> Note that I was running the SM on the target this time too.
>>>
>>> Which Linux distro was installed on the inititiator and on the target
>>> ? And if applicable, which OFED version ? Which kernel messages were
>>> logged by SRPT around the time the issue occurred (after having
>>> enabled SRPT logging first) ?
>>
>> As logging hadn't helped this issue previously, I've not been enabling
>> it.  That plus the kernel hacks needed to invoke logging, it's not
>> worth enabling.
>>
>> This was with Ubuntu 8.10, built-in IB on the 2.6.27-14-server kernel.
>>
>> I couldn't get ramdisks working w/ SCST in RHEL5.2.  When running:
>>
>> echo "open ramdisk /mnt/foo" > /proc/scsi_tgt/vdisk/vdisk
>>
>> I get the error:
>>
>> dev_vdisk: ***ERROR***: Wrong f_op or FS doesn't have required
>> capabilities
>>
>> ... which doesn't occur in the Ubuntu kernel, so I've been unable to
>> test RHEL kernels w/ ramdisks.  In general, this problem occurs w/ 8KB
>> and smaller blocks w/ the Ubuntu kernels, and 2KB and smaller blocks
>> w/ RHEL kernels.
>
> Use ramfs instead.

Do you mean:

mount -t ramfs -o size=7g ramfs /mnt/

?

That's what I'm doing.

Chris
>
>> Chris
>>>
>>> Bart.
>>>
>>
>>
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>
>