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#1 2013-04-06 21:12:15

student975
Member
From: Russian Federation
Registered: 2011-03-05
Posts: 603

poor SSD performance and scheduling - why?

Hi!

At first - yes, I have read the wiki smile I have got installed https://wiki.archlinux.org/index.php/SS … ITY3_120GB SSD (but 240GB rather 120GB). /etc/fstab has options "defaults,noatime,discard", file system is ext4. All three standard IO schedulers were tried. Two problems take place:

1. All that tests give me results 1.5-2 times worser (in that order: 9800/222, 252, 241, 5.9).
2. Scheduling: on heavy IO (installing libreoffice, for example): say, firefox hangs (clicking on some href does nothing) on waiting for pacman session completion.

Where to dig in further? Or - how to workaround? Hey, linux-ck users, are you here?
But it would be better to stay on the official kernel wink


"I exist" is the best myth I know..

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#2 2013-04-06 21:24:00

graysky
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From: The worse toilet in Scotland
Registered: 2008-12-01
Posts: 8,649
Website

Re: poor SSD performance and scheduling - why?

Not sure... is your setup SATA 3.0 Gb/s or SATA 6.0 Gb/s?  What is your motherboard?  If it is SATA 6.0 Gb/s, are you sure the SDD is connected to the faster controller?  Many boards (like my P8Z77-V Pro) offer only a 2x SATA 6.0 Gb/s connections.  Are you using a quality SATA 6.0 Gb/s rated cable?

Which I/O scheduler are you using?  Note that the ck1 patchset deals mainly with CPU scheduling, not I/O scheduling.


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#3 2013-04-06 21:35:44

student975
Member
From: Russian Federation
Registered: 2011-03-05
Posts: 603

Re: poor SSD performance and scheduling - why?

graysky, thanks, the stream speed magic is resolved: I have looked in motherboard documentation and have discovered SATA controller is 3 Gb/s only.


"I exist" is the best myth I know..

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#4 2013-04-06 21:48:01

student975
Member
From: Russian Federation
Registered: 2011-03-05
Posts: 603

Re: poor SSD performance and scheduling - why?

graysky wrote:

Which I/O scheduler are you using?

As I have mentioned, I have tried all standard ones: cfq, noop and deadline with the same result. Yes, I have checked selected scheduler was selected smile


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#5 2013-04-06 21:53:39

graysky
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From: The worse toilet in Scotland
Registered: 2008-12-01
Posts: 8,649
Website

Re: poor SSD performance and scheduling - why?

student975 wrote:
graysky wrote:

Which I/O scheduler are you using?

As I have mentioned, I have tried all standard ones: cfq, noop and deadline with the same result. Yes, I have checked selected scheduler was selected smile

Yes, you did.  Missed that.

student975 wrote:

graysky, thanks, the stream speed magic is resolved: I have looked in motherboard documentation and have discovered SATA controller is 3 Gb/s only.

OK!  Did the numbers change?  Usually, if two SSDs (same model) are offered in different capacities, the larger of the two is typically faster per the manufacture specs anyway.


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#6 2013-04-06 22:01:20

student975
Member
From: Russian Federation
Registered: 2011-03-05
Posts: 603

Re: poor SSD performance and scheduling - why?

graysky wrote:

OK!  Did the numbers change?  Usually, if two SSDs (same model) are offered in different capacities, the larger of the two is typically faster per the manufacture specs anyway.

Unfortunately all six SATA connectors are 3 Gbit/s.


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#7 2013-04-06 22:07:40

graysky
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From: The worse toilet in Scotland
Registered: 2008-12-01
Posts: 8,649
Website

Re: poor SSD performance and scheduling - why?

There is a difference in my experience which likely accounts for the numbers you posted.

Summary on my OCZ_Vertex 4 (128 GB):

 SATA 6.0 Gb/s vs. 3.0 Gb/s
Cached reads : 16,901 MB/s vs. 7,930 MB/s
dd writes 1  : 367 MB/s vs. 251 MB/s
dd writes 2  : 430 MB/s vs. 284 MB/s

Last edited by graysky (2013-04-06 22:09:24)


CPU-optimized Linux-ck packages @ Repo-ck  • AUR packagesZsh and other configs

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#8 2013-04-06 22:10:20

student975
Member
From: Russian Federation
Registered: 2011-03-05
Posts: 603

Re: poor SSD performance and scheduling - why?

graysky wrote:

There is a difference in my experience which likely accounts for the numbers you posted.

Summary on my OCZ_Vertex 4 (128 GB):

 SATA 6.0 Gb/s vs. 3.0 Gb/s
Cached reads : 16,901 MB/s vs. 7,930 MB/s
dd writes 1  : 367 MB/s vs. 251 MB/s
dd writes 2  : 430 MB/s vs. 284 MB/s

Yes, it's close to my results.


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