> Here's my first pass at a VM requirements document,
> for the embedded, desktop, and server cases. At the end is
> a summary of general rules that should take care of all of
> these cases.
>
> Bandwidth Descriptions:
>
> immediate: RAM, on-chip cache, etc.
> fast: Flash reads, ROMs, etc.
Flash reads aresometimes pretty slow. (Flash over IDE over PCMCIA...2MB/sec
bandwidth. Slower than most harddrives.
> medium: Hard drives, CD-ROMs, 100Mb ethernet, etc.
CDroms are way slower than harddrives (mostly to seek times).
> slow: Flash writes, floppy disks, CD-WR burners
> packeted: Reads/write should be in as large a packet as possible
>
> Embedded Case
> -------------
>
> Overview
> --------
> In the embedded case, the primary VM motiviation is to
> use as _little_ caching of the filesystem for reads as
> possible because (a) reads are very fast and (b) we don't
> have any swap. However, we want to cache _writes_ as hard
> as possible, because Flash is slow, and prone to wear.
>
> Machine Description
> ------------------
> RAM: 4-64Mb (reads: immediate, writes: immediate)
MB not Mb. 4Mb = 0.5MB.
> Flash: 4-128Mb (reads: fast, writes: slow, packeted)
> CDROM: 640-800Mb (reads: medium)
> Swap: 0Mb
>
> Motiviations
> ------------
> * Don't write to the (slow,packeted) devices until
> you need to free up memory for processes.
> * Never cache reads from immediate/fast devices.
Flash connected over PCMCIA over IDE is *very* slow. You must cache it.
-- Philips Velo 1: 1"x4"x8", 300gram, 60, 12MB, 40bogomips, linux, mutt, details at http://atrey.karlin.mff.cuni.cz/~pavel/velo/index.html.- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/