[Stgt-devel] Performance of SCST versus STGT

[Vladislav Bolkhovitin]

Erez Zilber wrote:
> FUJITA Tomonori wrote:
> 
>>On Thu, 17 Jan 2008 12:48:28 +0300
>>Vladislav Bolkhovitin <vst at vlnb.net> wrote:
>>
>>  
>>
>>>FUJITA Tomonori wrote:
>>>    
>>>
>>>>On Thu, 17 Jan 2008 10:27:08 +0100
>>>>"Bart Van Assche" <bart.vanassche at gmail.com> wrote:
>>>>
>>>>
>>>>      
>>>>
>>>>>Hello,
>>>>>
>>>>>I have performed a test to compare the performance of SCST and STGT.
>>>>>Apparently the SCST target implementation performed far better than
>>>>>the STGT target implementation. This makes me wonder whether this is
>>>>>due to the design of SCST or whether STGT's performance can be
>>>>>improved to the level of SCST ?
>>>>>
>>>>>Test performed: read 2 GB of data in blocks of 1 MB from a target (hot
>>>>>cache -- no disk reads were performed, all reads were from the cache).
>>>>>Test command: time dd if=/dev/sde of=/dev/null bs=1M count=2000
>>>>>
>>>>>                             STGT read             SCST read
>>>>>                          performance (MB/s)   performance (MB/s)
>>>>>Ethernet (1 Gb/s network)        77                    89
>>>>>IPoIB (8 Gb/s network)           82                   229
>>>>>SRP (8 Gb/s network)            N/A                   600
>>>>>iSER (8 Gb/s network)            80                   N/A
>>>>>
>>>>>These results show that SCST uses the InfiniBand network very well
>>>>>(effectivity of about 88% via SRP), but that the current STGT version
>>>>>is unable to transfer data faster than 82 MB/s. Does this mean that
>>>>>there is a severe bottleneck  present in the current STGT
>>>>>implementation ?
>>>>>        
>>>>
>>>>I don't know about the details but Pete said that he can achieve more
>>>>than 900MB/s read performance with tgt iSER target using ramdisk.
>>>>
>>>>http://www.mail-archive.com/stgt-devel at lists.berlios.de/msg00004.html
>>>>      
>>>
>>>Please don't confuse multithreaded latency insensitive workload with 
>>>single threaded, hence latency sensitive one.
>>>    
>>
>>Seems that he can get good performance with single threaded workload:
>>
>>http://www.osc.edu/~pw/papers/wyckoff-iser-snapi07-talk.pdf
>>
>>
>>But I don't know about the details so let's wait for Pete to comment
>>on this.
>>
>>Perhaps Voltaire people could comment on the tgt iSER performances.
>
> We didn't run any real performance test with tgt, so I don't have
> numbers yet. I know that Pete got ~900 MB/sec by hacking sgp_dd, so all
> data was read/written to the same block (so it was all done in the
> cache). Pete - am I right?
> 
> As already mentioned, he got that with IB SDR cards that are 10 Gb/sec
> cards in theory (actual speed is ~900 MB/sec). With DDR cards (20
> Gb/sec), you can get even more. I plan to test that in the near future.

Are you writing about a maximum possible speed which he got, including 
multithreded tests with many outstanding commands or about speed he got 
  on single threaded reads with one outstanding command? This thread is 
about the second one.

> Erez
> -
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