Hans Reiser wrote: > I have a US customer who needs work done that involves figuring out why > the kernel/filesystem/hard drive adds pauses that cause video glitches.
Welcome to the club :-) We're working on fairly similar issues in the ABISS project, http://abiss.sourceforge.net/ > This is much deeper and harder than you would guess, and involves > elevator work, filesystem work, vm work, working hand-in-hand with disk > drive vendors to do things I can't talk about here yet, etc. There may > be work involving block allocators optimized for streaming media, > resizer work, repacker work, etc. I can guess :-) Your shopping list looks similar to ours. I think we've pretty much covered the elevator side. Our proof of concept elevator does priorities and a number of related things. This is synchronized with Jens' work, so these features should eventually show up in CFQ and the block IO layer. (At which point the ABISS elevator shall be unceremoniously scrapped.) VM work is lined up next. So far, the most promising approach for getting rid of VM interference seems to be to base things on the NUMA infrastructure. We currently support "real-time" reading from FAT, VFAT, ext2, and ext3. There are also some scary things we can do for writing, such as messing with the block allocation strategy (*). The latter are currently only for FAT and VFAT. (*) Doing file system brain surgery at this level may be a dead end. Just getting the various file systems to support reservations or an equivalent way for obtaining large contiguous allocations looks like a much nicer approach. As far as doing unspeakable things with drive manufacturers is concerned, control over defect management and thermal calibration come to mind. Zoning and noise management details may also be of interest. I'm not sure how deep you really want to go there. I'd expect that by selecting reasonably well-behaved drives and just measuring what they do, a useful performance envelope could be determined, that will allow you to provide adequate buffering and/or prefetching to cover the occasional drive hickup. - Werner -- _________________________________________________________________________ / Werner Almesberger, Buenos Aires, Argentina [EMAIL PROTECTED] / /_http://www.almesberger.net/____________________________________________/
