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

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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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