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

[Vladislav Bolkhovitin]

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.

> Chris
>> Bart.
>>
> 
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