[Stgt-devel] No LUN option in target.c

[Tomasz Chmielewski]

FUJITA Tomonori schrieb:
> On Mon, 26 Nov 2007 13:33:47 +0100
> Tomasz Chmielewski <mangoo at wpkg.org> wrote:
> 
>> FUJITA Tomonori schrieb:
>>> On Mon, 26 Nov 2007 12:25:19 +0100
>>> Albert Pauw <albert.pauw at gmail.com> wrote:
>>>
>>>> 2007/11/26-12:24:19 | STAT  | 3237 | v1.2.8 | /dev/sdb | Total read 
>>>> throughput: 827938.1B/s (0.79MB/s), IOPS 25.3/s.
>>>>
>>>> The patch didn't make a difference, sorry.
>>> The performances in the configuration don't matter much, but I just
>>> run initiator and target on the same machine:
>>>
>>> sens:/home/fujita# hdparm -t /dev/sdd
>>>
>>> /dev/sdd:
>>>  Timing buffered disk reads:   20 MB in  3.15 seconds =   6.35 MB/sec
>> (...)
>>
>>> sens:/home/fujita# hdparm -t /dev/sdd
>>>
>>> /dev/sdd:
>>>  Timing buffered disk reads:  410 MB in  3.02 seconds = 135.55 MB/sec
>>>
>>>
>>> Seems that haparm isn't an appropriate tool to meature performance but
>>> not bad performances.
>> It is appropriate, when used appropriately.
> 
> Oops, I'm not talking about only cache.
> 
> hdparm seems to issue only one outstanding request, the duration is
> too short, etc. It's not designed for performance measurement.

True, hdparm is only a very basic tool for measuring performance.


>> If a block device is used (mounted, swap, md/dm etc.) it is also cached.
> 
> Block devices always use page cache (unless you access to it via DIO).

Umm:


# echo 3 > /proc/sys/vm/drop_caches

# free
              total       used       free     shared    buffers     cached
Mem:        512252      22152     490100          0         84       4320
-/+ buffers/cache:      17748     494504
Swap:            0          0          0

# dd if=/dev/LVM2/swap of=/dev/null
6291456+0 records in
6291456+0 records out
3221225472 bytes (3.2 GB) copied, 52.8739 seconds, 60.9 MB/s

# free
              total       used       free     shared    buffers     cached
Mem:        512252      22760     489492          0        124       4708
-/+ buffers/cache:      17928     494324
Swap:            0          0          0

So, nothing was cached.

Now, let's use this volume:

# swapon /dev/superthecus/swap

# dd if=/dev/superthecus/swap of=/dev/null
6291456+0 records in
6291456+0 records out
3221225472 bytes (3.2 GB) copied, 52.4117 seconds, 61.5 MB/s

# free
              total       used       free     shared    buffers     cached
Mem:        512252     423212      89040          0     393836       4348
-/+ buffers/cache:      25028     487224
Swap:      3145720        112    3145608

Plenty of cache was used.

So, once dd accessed it via DIO, and once without DIO? I don't 
understand it.


> BTW, please let me know if you find that tgt's performance is still
> terrible as compared with IET.

Yes, I'll try to make some tests this week.



-- 
Tomasz Chmielewski
http://wpkg.org