Messages in this thread | | | Subject | Re: Queues when accessing disks | From | "M. Edward Borasky" <> | Date | Fri, 31 Dec 2004 12:26:44 -0800 |
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On Fri, 2004-12-31 at 04:32 +0100, Felipe Erias wrote: > Hi, > > I'm trying to apply queuing theory to the study of the GNU/Linux kernel. > Right now, I'm focusing in the queue of processes that appears when they > try to access an I/O device (specifically, an IDE HD). When they want to > read data, it behaves as a usual queue: several clients (processes) that > require attention from a server (disk / driver / ...). The case when they want > to write data is a bit more tricky, because of the cache buffers used by the OS, > and maybe could be modelized by a network of queues. Both cases are > interesting for my work, but I'll take the reading one first, just > because it seems > a bit more simple 'a priori'. > > To modelize the queue, I need to get some information: > - what processes claim attention from the disk > - when they do it > - when they begin to be served > - when they finish being served > > To get all this information, maybe I could hack my kernel a bit to write > a line to a log on every access to the HD, or account the IRQs from > the IDE channels... I also have the feeling that this queuing problem could > dissappear o became more hidden if DMA were enabled. > > To be true, I'm a bit lost and that's why I ask for your help. > > Yours sincerely, > > Felipe Erias
I have a similar goal -- building an operational queueing model of a running Linux system. At this point, though, I'm not really trying to do per-process work, just model the system overall, including processors, I/O and virtual memory. As I noted in a recent posting, I'm currently blocked by the incorrect statistics gathered by a 2.4 kernel in "/proc/partitions". You can compute the throughputs, but not the average wait and service times, or the utilizations, which depend on the service times.
I'm rather strongly considering establishing a mailing list just devoted to this topic -- queuing models of Linux kernels based on statistics the kernel collects. If such a list already exists, please let me know -- I don't want to re-invent any wheels, but there *is* a wheel I do want to invent! Please e-mail me off-list if you know of such a list or would join in if I create it.
Thanks,
Ed Borasky http://www.borasky-research.net/
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