Thread: Boost N900! :)
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Posts: 436 | Thanked: 406 times | Joined on Jan 2010
#297
Originally Posted by retsaw View Post
What research did you do into this? Was it just changing and observing that it made the computers you tested faster, or was there more to it than that?

While investigating the function of each of the settings that swappolube changed, I had a hard time finding much information on this one, so I ended up digging around in the kernel source code, and there was a comment saying that even though there are performance benefits from larger values for systems with larger amounts of RAM there were negative effects from setting this value above 3, so the default for a vanilla kernel is 3 (or 2 on very low memory systems), however there was no indication as to what the negative effects were in the comments. This value is used both for the number of swap pages to read ahead, as well as the number of swap pages to write in one go, it also uses the number in the 2^n fashion, so a value of 6 indicates 64 pages. Higher values are mostly of use when swap is on a hard disk drive where seek time is an issue, so it is beneficial to group read/writes into larger chunks to reduce the amount of time spent seeking. On an SSD seek times are less of an issue, so I would expect less of a benefit from high values, I would also think that lower values would tend to reduce lagginess when writing to swap since it will be doing it in smaller chunks. But to be honest I don't truly know how this affects responsiveness on the N900 and what is the best way to go.

Personally I decided to heed the warning and set it to 3, while swappolube sets it to 0 (IIRC).
Actually most of the patch is simply personal hack I made after looking into pulse audio and observing the file systems and the various functions in the device.

Basically there was a thread in this forum speaking about pulse audio being a bad choice for the n900 because of cpu consumption and what not....it peaked my interest and I decided to look into it, did some research into the various pulse audio files, (mainly alsa mixer) began changing things up...and thats it

About page cache....lowering the value makes the system slower, this I know for certain. The n900 needs swap for most things. Swap uses page-cache to perform more efficiently.

The default value is 5, I turned it up to 6 just to make things relating to swap a little more efficient.

Things were notably slower with page-cache set to 0 in all my tests.

The best way to go is to actually leave it at "5".

Last edited by SavageD; 2010-12-10 at 03:00.
 

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