[haiku-development] Re: Writing Device Drivers - CRAM - Problem uninit_driver()

  • From: Earl Pottinger <earl_colby_pottinger@xxxxxxxxx>
  • To: haiku-development@xxxxxxxxxxxxx
  • Date: Mon, 22 Aug 2011 13:35:10 -0700 (PDT)

> From: Stephan Aßmus <superstippi@xxxxxx>
> Subject: [haiku-development] Re: Writing Device Drivers - CRAM - Problem 
> uninit_driver()

> > 1) Compression: this let`s me hold a far larger
> percentage of the drive image in ram than Haiku`s cache.
> If it's so beneficial, maybe Haiku's disk caching should
> also use compression?

Depends, I tune my compression code to the main contents of the ramdisk, I use 
a version of LZ that works nicely on text.  But I am looking at other 
compressors that are tuned for object code.  As an optional feature I think it 
could be a good idea.
> > 2) Pre-loading: this means on the solid image (single
> file) version of the ramdisk I just boot and all the data
> contained in the ramdisk is loaded by the time booting has
> finished.

> That sounds like only the times are shifting around: Isn't
> your boot time much slower as a result?

Yes, but a single 256MB file adds 2 seconds to my boot time period.  And then 
it is just there to use.

> > 3) Fake-Raid: the purpose is not to protect your data
> or make access faster.  What is gain is the ability to
> treat a bunch of drives as a single drive, whit it`s size
> being the sum of the size of the individual drives.
> If the purpose is to chain some disks together to sum up
> their size, how does a RAM disk help, which is limited to
> around 2GB?

This ramdisk (versions 0.40 and greater) CAN be set to a size greater than 
available memory, and then pages out it`s extra data tracks to the different 
drives.  At this point you gain in size of the drive at the expense of losing 

> > 4) Speed: I did some very simple speed tests, there is
> only a small boost in speed compared to my Intel SSD. 
> But I see a big difference between my ramdisk and my IDE
> 40GB drives.

> That argument sounds strange to me.

You could be very very right.  There is a reason I said simple tests.

Give me a little time and I will do some proper bench-marking.

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