SD Card read ahead speed change (from xda)

[Guest ms20]

http://forum.xda-developers.com/showthread.php?t=1010807

I saw this on xda portal and changed the file size from 128 to 3072 which has vastly increased read speed according to SD Tools from the market

I did this on cm7 nightly 34

There's loads more info through the link ^

[Guest Ron=)]

http://forum.xda-developers.com/showthread.php?t=1010807

I saw this on xda portal and changed the file size from 128 to 3072 which has vastly increased read speed according to SD Tools from the market

I did this on cm7 nightly 34

There's loads more info through the link ^

Thank you for sharing.. will definately check that out!

[Guest Colcut]

Very cool I'm seeing an increase of 4MB/s on write and 15MB/s on read.

I tried with 4096 and the speed didn't increase, then tried 3072 and the speed was there!

[Guest LVL91]

Looks promising...

Gonna give it a try!

[Guest ms20]

Try the Gallery app - pictures load pretty much straight away

[Guest Frankish]

My speeds went down. What's all that about?

[Guest ninzor]

I ran a test with CM7 RC4 and I got 8.2MB/s write speed and something 80MB/s read speed, so I ain't changing a thing.

[Guest tcpaulh]

Wow, I mean WOW!

Using the cheap play.com 16gb sd card speeds went from 4.5/11.1 to 6.3/58.6. Yes, 58.6.

Oh, I went with 3072 from default 128 on cm7 n35

Edited April 4, 2011 by tcpaulh

[Guest exec]

Increased read from 8MB/s to 70MB/s. Gallery loading is fast as hell now, thanks!

[Guest Flumpster]

Same results here.. Fibbs 11b and the 3072 option. Went from around 10-11 read speed upto 50+

Nice find :D

[Guest andycanada]

write speed didn't improve but read speed increased 5 times!

thanks

[Guest steveuk1981]

How do you do this? do you just download http://forum.xda-developers.com/showpost.p...p;postcount=122 one of those files and flash it via clockwork ?

[Guest frenchdroid]

Thanks for sharing the link to the thread on this.

I don't understand how come, but my write speeds seem to have increased too - from 4 to about 6.5, and the read speed went from 11 to about 85.

This is just on a lowly class 2 Sandisk 16 gb card (running CM7 N32).

I hope it makes a difference in real world use.

[Guest JobSup]

I don't understand how come, but my write speeds seem to have increased too - from 4 to about 6.5, and the read speed went from 11 to about 85.

This is just on a lowly class 2 Sandisk 16 gb card (running CM7 N32).

I also tried it on my Sandisk 16gb Class 2 (probably the same card, used the 2048kb setting). Write speed stays around 8 MB/s, but the read speed increased from approx 10MB/s to 80MB/s. Great difference here!

Anyway, the results only give you a rough idea. Just run the tests several times and you will see. But the jump from 10MB/s to 80MB/s will make a difference when accessing data on the SD card.

Thanks

[Guest dandroidme]

The effect will entirely depend on what you are doing with the card.

And you need to add in the effect of the file system block size (which will change) and also the flash controller's block size (which you probably don't know)

read / write a lot of huge contigious data blocks (e.g. video streaming with a blank card or, err... badly written SD card speed test programs) -> faster.

read / write a lot of small files spread out over the file system (normal usage) -> slower.

Mucking around with the sizes of caches and read/write buffers usually has very variable results - Notwithstanding the manufacturer getting it badly wrong in the first place.

d.

Edited April 5, 2011 by dandroidme

[Guest rak007]

Me too got around 81 Mb/s read speed after keeping cache as 4096.

[Guest Maxxo]

Working good so far, thank you

Before: 16 / 76.7

After: 22 / 85.4 (3072)

[Guest The Soup Thief]

The effect will entirely depend on what you are doing with the card.

And you need to add in the effect of the file system block size (which will change) and also the flash controller's block size (which you probably don't know)

read / write a lot of huge contigious data blocks (e.g. video streaming with a blank card or, err... badly written SD card speed test programs) -> faster.

read / write a lot of small files spread out over the file system (normal usage) -> slower.

Mucking around with the sizes of caches and read/write buffers usually has very variable results - Notwithstanding the manufacturer getting it badly wrong in the first place.

d.

I've been checking read/write speeds with AnTuTu benchmark and am getting much more modest improvements in R/W speeds at each of the cache sizes. With the same cache sizes SD Tools registers comparable read speeds, but write speeds many times faster than AnTuTu. Not sure either is a more useful measure - it just highlights the vagaries of measurement

Don't suppose Dandroidme or anyone else can suggest a compromise cache size to offer the best usability overall?

I'd guess it might be somewhere in the middle - 1024 or 2048, but that is just a guess

Edited April 5, 2011 by The Soup Thief

[Guest dandroidme]

The answer is... it's complicated.

What you must factor in is that the transfer speed will be affected by:

1) How the application requests access the the card (see e.g. differences between test programs)

2) how the file system caches the requests from the application

3) How the device driver caches requests from the file system (that's what we are changing here)

4) The SD card's flash controller's preferred access size (changes when you change card)

5) The topology of the card - how it is formatted, how much free space, how much fragmentation

...and these all interact with each other.

The problem is you can "tune" any one of these for a particular use case, show spectacular improvements and at the same time ruin everything else.

Given that I'd say - leave it as it is!

d.

Edited April 5, 2011 by dandroidme

[Guest dandroidme]

Re-reading the XDA thread, 128K is probably plenty at the device driver level.

I'll go out on a limb and say I really doubt there will be much real-world improvement increasing this.

I'd further go out on a limb and say you could show significant improvements in many use cases by reducing it to the derided 4K mentioned in the XDA thread.

(crosses fingers / ducks)

d.

Edited April 5, 2011 by dandroidme

[Guest eucurto]

Good tip! i got great improvement in opening pictures in Gallery. (2048)

[Guest Mushroom_Lord]

Pretty sure gallery isnt faster for me.

3072

691mhz cpu

32mb vm

cm7

EDIT: NOW I think it is :D

Edited April 5, 2011 by Mushroom_Lord

[Guest wbaw]

/sys/devices/virtual/bdi/31:0/read_ahead_kb

I think this is the same setting for the internal nand.

[Guest tcpaulh]

/sys/devices/virtual/bdi/31:0/read_ahead_kb

I think this is the same setting for the internal nand.

Interesting. Now, what benchmarking strategy? Bootup times?

[Guest simonsays1]

I tried this mod and got some good results using 2048, but then I downloaded the new version of SD tools and my speed seems to have gone slow again ?