Linux slowdown on 20M - summary

Pavel Machek (
Fri, 25 Apr 1997 15:11:55 +0200


[I'm now connected via cslip on 2400 modem, so sorry for bad formating/

I recently posted results of some tests - consisting of compilation of
2.1.35 kernel on 2.1.35 linux. Everything on 486DX2/80 with
20MB of ram.

On 20MB of ram, it took 32 minutes (128k l2 enabled)
on 16MB of ram (or with mem=16M option) it took
22 minutes (with l2 cache enabled).

Everyone told me that it is HW problem because my high 4MB of ram
are not cacheable.
So I turned level 2 cache off completely.

COmpile time with mem=16M was 30 minutes,
with 20MB of ram it was 35 minutes.

So problem still exists with l2 disabled.

[It still may be hw, however]

Other think I noticed is that time from Uncompressing kernel to Elf:login differs heavily (15 sec X 25 sec) with 16MB and 20MB
of memory (16MB is faster). Also 'interactive performance' is much
worse with 20MB.
Both even if l2 disabled.

Other ideas (beside of cache problems were:)

Problems with disk access not possible to memory higher that 16MB directly -
impossible since I do not use DMA on disks and since disk activity when
compiling kernel is almost none.
David (?) Told me something about inode cache.