CPU scheduling (by alaric)

I came across the original paper on Lottery Scheduling.

What was all the fuss about? All it boils down to is using a weighting assigned to each process to divide time between CPU-bound processes at the same priority level. Back when I was a kid and wrote my first preemptive multitasking kernel, that's what I did, because being a lame MS-DOS programmer I hadn't thought of blocked processes being removed from the run queue, and I thought that 'priority' must be such a weighting.

Anyway, it got me thinking. Lottery scheduling is fine for long-running non-real-time processes at the same priority. A user running a few background computational tools such as distributed.net and SETI@Home would benefit from being able to choose the balance between the two at will, sure. But for event-driven tasks like a GUI frontend, a classic priority scheme would still win, if people bothered to set the priorities correctly. As it stands, unless they explicitly make a process 'nice', they usually just leave it to the OS to dynamically assign priority based upon the processes' I/O behaviour, using adaptive heuristics that take a while to respond to changes in the behaviour anyway.

And the inefficincies of this approach are often seen when some heavyweight background computation causes your GUI to become unresponsive... Read more »

plasticbag.org | weblog | The New Musical Functionality: Portability and access (by alaric)

plasticbag.org | weblog | The New Musical Functionality: Portability and access

My take on all this is that portable music, mobile phones, and PDAs and so on will inevitably converge into a general purpose portable computer.

On the desktop, general purpose PCs do everything; even the humble desk telephone is finally being subsumed by the PC with VoIP, a process that started in the 1990s but was somewhat humbled by the cost of a voice modem on every machine over a standard telephone not being sufficiently counterbalanced by advantages.

And I hate having too many pocket gadgets to carry around that (shudder) all need plugging in to recharge. Now that people are used to mastering the complexities of a general purpose computer on their desktop, I don't see any reason why a general purpose pocket computer, that (via some combination of inbuilt facilities and tiny plugin modules) can contact a mobile telecommunications network, send digital audio to your ear, and store lots of data. Read more »

Log structured file systems (by alaric)

My current drafts for the implementation of TUNGSTEN need some form of log structured file system beneath it all to efficiently and safely implement transactions.

This article looks promising:

http://tlb.org/papers-usenixw95.html

Research results show that while Log-Structured File Systems (LFS) offer the potential for dramatically improved file system performance, the cleaner can seriously degrade performance, by as much as 40% in transaction processing workloads. Our goal is to examine trace data from live file systems and use those to derive simple heuristics that will permit the cleaner to run without interfering with normal file access. Our results show that trivial heuristics perform very well, allowing 97% of all cleaning on the most heavily loaded system we studied to be done in the background.

Broken file server 3 (by alaric)

Eeeeeaaarrrrggghhh

I won't go into the details, but a slip of the mind while juggling my partitions around to try to get the machine booting again has resulted in me accidentally laying a new root partition that overlaps my home directory partition.

After newfs-ing the new root partition, then realising my mistake, I've found that the home partition is still mountable, but a little worse for wear for having had cylinder group headers and backup superblocks and whatnot dropped all over it (but, thankfully, no file data since it's RIGHT at the end of the disk).

I've got an old backup, and I've been gingerely picking around the remnants of the filesystem (having dd-ed it to a file and mounted it via a vnode device) and picking up stuff that's changed since the backup.

Ok, I've lost my archive of files I'd downloaded. Which is bearable. I didn't keep them backed up because they're huge.

But I've also lost the accounts for Warhead.org.uk Ltd. I've got a version that's out of date, but now I've got to do a lot of cross-referencing other things to put back all the transactions that have happened since.

This will be mind-bogglingly dull. I'm not a happy bunny...

Broken file server update (by alaric)

I've tried blanking the primary disk and reinstalling from scratch.

No luck - it's still not booting, with exactly the same symptoms.

Could it be a problem with the disk? My machine can boot a kernel from floppy, after all. Although the floppy kernel is one that's designed to be small enough to fit on a floppy, so it could be a memory problem prohibiting large kernels from running.

Well, for my next trick, I'll try a different hard disk. I don't think I have any as big as the current one lying around, however, so it'll have to mean running with a smaller disk. Oh, well...

Wish me luck 🙁