Re: 2.5.2-pre performance degradation on an old 486

From: Matthias Hanisch (
Date: Sat Jan 05 2002 - 03:25:48 EST

On Sat, 5 Jan 2002, Mikael Pettersson wrote:

> When running 2.5.2-pre7 on my old for-testing-only 486(*),
> file-system accesses seem to come in distinct bursts preceded
> by lengthy pauses. Overall performance is down quite significantly
> compared to 2.4.18pre1 and 2.2.20pre2. To measure it I ran two
> simple tests:
> Test 1: time to boot the kernel, from hitting enter at the LILO
> prompt to getting a login prompt
> Test 2: time to "rm -rf" a clean linux-2.4.17 source tree, using
> the newly booted kernel (no other access to the tree before that,
> so it wasn't cached in any way, and the machine was otherwise idle)
> Test 1 Test 2
> 2.2.21pre2: 71 sec 75 sec
> 2.4.18pre1: 64 sec 72 sec
> 2.5.2-pre7: 97 sec 251 sec
> I haven't noticed any slowdowns on my other boxes, so I didn't
> do any measurements on them. On the 486 it's very very obvious.

This is exactly, what I see with my old 486 box. It started with
2.5.2-pre3, which contained two major items:

- bio changes from Jens
- scheduler changes from Davide

Surprisingly, backing out the bio changes didn't help. Backing out the
scheduler changes from Davide did!!

Maybe the problem lies somewhere in between, because it is often I/O
related, e.g. first call of ldconfig is horrible slow, as is e2fsck.

But I also see system hiccups from time to time, where console switching
does not work for 1 second on an idle box.

> (*) 100MHz 486DX4, 28MB ram, no L2 cache, two old and slow IDE disks,
> small custom no-nonsense RedHat 7.2, kernels compiled with gcc 2.95.3.

Is this ISA (maybe it has something to do with ISA bouncing)? Mine is:

486 DX/2 ISA, Adaptec 1542, two slow scsi disks and a self-made
slackware-based system.

Can you also backout the scheduler changes to verify this? I have a
backout patch for 2.5.2-pre6, if you don't want to do this for yourself.

        Matze (trying 2.5.2-pre8 now)

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