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SubjectRe: Abysmal interactive performance on 2.4.linus
On Mon, 12 Nov 2001, Frank de Lange wrote:

> On a 768 MB SMP box (2x466 MHz Celeron), I see some weird problems with
> interactive performance on 2.4.15pre{1,2}. A good example of this is the
> following scenario:
>
> - copy a large file (eg. an iso image file) to a directory on the same
> (reiserfs in this case) filesystem, or...
> - do a filesystem comparison between a CD and the original file (with cmp
> /mnt/cdrom/<filename> /mnt/reiserfs/1/data/<original_file_location>, using a
> PLEXTOR Model: CD-ROM PX-40TS SCSI CD-ROM drive),
>
> - and THEN (while the copy or comparison runs) try any simple command (like
> 'ls /mnt/reiserfs/1/data' or 'top' or anything else...).
>
> Response time is abysmal, a simple 'ls /some/dir' takes tens of seconds to
> start. Once the command is running, performance is normal. Try this when a
> cdrecord session is running and you'll get a buffer underrun.
>
> The box has 768 MB of RAM, 512 MB of swap. There is no significant load on the
> system (according to an already running copy of top) neither before nor during
> the test. Try tab-completing a command in a terminal, and that terminal freezes
> for tens of seconds, usually until after the file system load has gone down.
>
> In a few words, heavy filesystem activity seems to wreak havoc on the system.
> Not by loading the CPU (it hardly breaks out a sweat at 178% idle (SMP...)).
>
> Turning off swap (swapoff -a) does not change the observed behaviour.
>
> Anyone else seen something like this?

I have 2.4.10-ac12 here and reiserfs filesystems and I have to say that
performance is terrible when doing anything diskintensive. It seems like
diskscheduling is very broken for my IDE disk, or it's a reiserfs
problem. maybe it pushes a _lot_ into the diskscheduling at once?

I've heard that read-ahead for IDE has been broken for a while but's fixed
in -ac and in Andre Hedrick's IDE-patches.

I'm going to upgrade to a more recent kernel and see how it behaves.

/Martin

Never argue with an idiot. They drag you down to their level, then beat you with experience.

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