linux-kernel - Re: [Scst-devel] [ANNOUNCE]: Comparison of features sets between different SCSI targets (SCST, STGT, IET, LIO)

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Message-ID: <49DA49AA.1060106@wpkg.org>
Date:	Mon, 06 Apr 2009 20:27:54 +0200
From:	Tomasz Chmielewski <mangoo@...g.org>
To:	Vladislav Bolkhovitin <vst@...b.net>
CC:	Bart Van Assche <bart.vanassche@...il.com>,
	linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org,
	iscsitarget-devel@...ts.sourceforge.net,
	James Bottomley <James.Bottomley@...senpartnership.com>,
	scst-devel <scst-devel@...ts.sourceforge.net>,
	stgt@...r.kernel.org
Subject: Re: [Scst-devel] [ANNOUNCE]: Comparison of features sets between
 	different SCSI targets (SCST, STGT, IET, LIO)

Vladislav Bolkhovitin schrieb:

>> Encrypted device was created with the following additional options 
>> passed to cryptsetup
>> (it provides the most performance on systems where CPU is a 
>> bottleneck, but with decreased
>> security when compared to default options):
>>
>> -c aes-ecb-plain -s 128
>>
>>
>> Generally, CPU on the target was a bottleneck, so I also tested the 
>> load on target.
>>
>>
>> md0, crypt columns - averages from dd
>> us, sy, id, wa - averages from vmstat
>>
>>
>> 1. Disk speeds on the target
>>
>> Raw performance: 102.17 MB/s
>> Raw performance (encrypted):  50.21 MB/s
>>
>>
>> 2. Read-ahead on the initiator: 256 (default); md0, crypt - MB/s
>>
>>                            md0   us  sy  id  wa  | crypt   us  sy  id  
>> wa  STGT                      50.63   4% 45% 18% 33% | 32.52    3% 62% 
>> 16% 19%
>> SCST (debug + no patches) 43.75   0% 26% 30% 44% | 42.05    0% 84%  1% 
>> 15%
>> SCST (fullperf + patches) 45.18   0% 25% 33% 42% | 44.12    0% 81%  2% 
>> 17%
>>
>>
>> 3. Read-ahead on the initiator: 16384; md0, crypt - MB/s
>>
>>                            md0   us  sy  id  wa  | crypt   us  sy  id  
>> wa  STGT                      56.43   3% 55%  2% 40% | 46.90    3% 
>> 90%  3%  4%
>> SCST (debug + no patches) 73.85   0% 58%  1% 41% | 42.70    0% 85%  0% 
>> 15%
>> SCST (fullperf + patches) 76.27   0% 63%  1% 36% | 42.52    0% 85%  0% 
>> 15%
> 
> Good! You proved that:
> 
> 1. SCST is capable to work much better than STGT: 35% for md and 37% for 
> crypt considering maximum values.
> 
> 2. Default read-ahead size isn't appropriate for remote data access 
> cases and should be increased. I slowly have been discussing it in past 
> few months with Wu Fengguang, the read-ahead maintainer.

Note that crypt performance for SCST was worse than that of STGT for 
large read-ahead values.
Also, SCST performance on crypt device was more or less the same with 
256 and 16384 readahead values. I wonder why performance didn't increase 
here while increasing readahead values? Could anyone recheck if it's the 
same on some other system?


> Which IO scheduler on the target did you use? I guess, deadline? If so, 
> you should try with CFQ as well.

I used CFQ.


-- 
Tomasz Chmielewski
http://wpkg.org
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