[Touch Pro2, Tilt 2 Android Development] Caldair:
These Following Settings Work For Me. Use Caution When Changing Frequencies On Your Device. I won't be responsible for damages.

A Strange thing about this tweak. I have been using SD Booster with all XDAndroid(haret) builds for about a year and always found that my best setting was 1536kb (my "sweet spot" if you will) based on benching with SD Tools, so I would have that value set at boot.

Recently I have been noticing (or finding it more annoying!) that when I go from doing one thing to another on my phone (eg. reading mail, close mail then check battery usage) there would be quite a noticeable hang while loading. So I set about thinking about possible bottlenecks when switching active processes and when I started to think about "reading ahead" on the SD (which in our case is our system drive) I thought "Why do I want to read ahead when the system doesn't know what I am going to do next?"

So I started to set the cache down to 128k and noticed that the system overall seemed snappier or more agile when going from task to task. Now this setting definitely yeilds a slower throughput when benching with SD Tools, but qualitatively I do not notice that it is actually any slower when loading/transferring large files etc.

This makes some sense to me if I look at it from the point of view that now the system is only reading ahead a small amount and is less likely to be busy reading data which it is not going to use when I request it to read in a different location. IE not maintaining a large bloated cache of potentially useless data.

I then decided that if a small cache worked better than a large one maybe maintaining no cache at all would be even better! Unfortunately though, the lowest setting that will stick when using SD Booster is 128k. So I edited my gingerbread.user.conf in /sdcard/conf/ and added the line:

echo 0 > /sys/devices/virtual/bdi/179:0/read_ahead_kb

This sets the cache to 0kb (it actually shows as error in SD Booster).

With this setting I find that the overall experience is greatly improved: Loading times(with the possible exception of ES File Explorer, but its always funny), closing times, switching active apps, home screen drawing (in fact all screen draws), incoming calls/texts/emails, installing apps from the market, and uninstalling apps all seem smoother and faster. Again though, my benchmarks with SD Tools are lower than with the cache set to 1536kb.... Until:

I added msmsdcc_fmax=48000000 to the cmdline section of startup.txt and overclocked the processor. At a clock speed of 614MHz(you can go higher!) I am able to beat ALL of my benchmarks while using a cache of ANY size and the highest possible stable clock speed(for me 768MHz)!

So to summarize I seem to get the best access to my SD with the Read Ahead Cache set to 0, the SD Card max freq set to 48MHz and the processor at least moderately overclocked.

Now I don't know what the system actually does when read_ahead_kb is 0. It would seem the only options are: a)No Cache b)A Default size Cache or c)A System Managed Dynamic Cache(less likely IMO).

It may be that I am crazy and that these performance gains are all in my head, but it does seem to be a major improvement to me. I am sure that having a large cache is optimum when your SD Card is used just as file storage, but we(haret users) use the SD as our system disk and I think that agility(random seek) is more important than straight forward linear speed.

If anyone else is brave enough to try playing around with these "tweaks" and could report their findings I would appreciate the feedback.

Just a little more information:

My hardware is Rhod100, running GBX0C, kernel version 3.3.8. My card is SanDisk 8GB Class 2.

I have also used VM Heap Tool to set my VM max heap size to 64Mb(this helps a lot when I use large apps like Puffin Browser) and am using Zeam Launcher(so I don't know how this affects the default launcher).

If I am doing anything that anyone feels is damaging and or just stupid please inform me of that too before I fry my baby!

Thanks everyone.