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

[Chris Worley]

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.

Chris
>
> Bart.
>