Hi! > 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 [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
