On Sun, 3 May 1998, Troels Arvin wrote:
> When the rc5des software is not running, the following procedure
> takes around one minute:
> time cat /dev/hda1 >/dev/null
> (CPU usage is around 30%)
Just out of curiosity... why are you doing this at all? :)
> hda1 is an IDE disk (PIO4) of around 360 MB. The rc5des client
> has no relation to the partition whatsoever (the partition
> is not mounted at all).
Are any other partitions on this disk mounted at the same time? What
about other drives on the same IDE controller? Have you tried this with
the rc5 client's output redirected to /dev/null? Do you notice any
unusual disk activity while the cat is trying to run?
BTW, the rc5 client always runs with the lowest possible priority no
matter what you set it to initially.
> Name: cat
> State: D (disk sleep)
This means that cat has blocked waiting for the disk. Disk-intensive
processes block on this a lot. So the question is not, what is the rc5
client doing, but the question really becomes, what is the disk doing?
> I consider the phenomenon as a potential denial-of-service
> problem: I think that a normal user should not be able to
Does the rc5 client affect normal file access in any particular way, or
only this use of the raw device file?
> Could this be a kernel bug? A glibc bug? Some other bug?
It is more likely to be a kernel bug than a glibc bug.
> Is there something utterly wrong with time-slicing to the
> IDE-controller?
No, but there are some fundamental limitations of the IDE system that can
cause this sort of thing. Particularly related to having two drives on
one IDE controller combined with a lot of disk access. It's worse if you
have a middle-aged motherboard circa 1994 or 1995, as most of these had
buggy IDE controllers.
> Could there be a connection between my observations? - The IDE
> throughput/priority/time-slicing problem and the
> non-responsive apache?
Possibly. Looking over your message I didn't see any references to bad
apache response. :) So I don't know.
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