Re: Serious Kernel slowdown with HIMEM (4Gig) in 2.6.7

[Darren Williams]

Hi Lawrence

On Fri, 13 Aug 2004, Lawrence E. Freil wrote:

> Hello,
>    
> I'm following the kernel bug reporting format so:
> 
> 1. Linux 2.6.7 kernel slowdown in directory access with HIMEM on
> 
> 2. I have discovered an issue with the Linux 2.6.7 kernel when HIMEM is
>    enabled which exhibits itself as a slowdown in directory access regardless
>    of filesystem used.  When HIMEM is disabled the performance returns to
>    normal.  The test I ran was a simple "/usr/bin/time ls -l" of a directory
>    with 3000 empty files.  With HIMEM enabled in the kernel this takes
>    approximately 1.5 seconds.  Without HIMEM it takes 0.03 seconds.  The
>    time is 100% CPU and no I/O operations are done to disk.  "time" reports
>    there are 460 "minor" page faults with zero "major" page faults.
>    I believe the issue here is the mapping of pages between high-mem and
>    lowmem in the kernel paging code.  This increase in time for directory
>    accesses doubles to triples times for applications using samba.
>    I have also tested this on another system which had only 512Meg of RAM
>    but with HIMEM set in the kernel and did not experience the problem.
>    I believe it only effects the performance when the paging buffers end
>    up in highmem.
> 
> 3. Keywords: HIMEM, Performance
> 
Would you be running these in a gnome-terminal, I remember seeing a thread
that discussed gnome-terminal problems though a quick search did not turn
anything up. Here is what I get between a xterm and gnome-terminal.

xterm
# time ls -lR /etc
real    0m0.381s
user    0m0.056s
sys     0m0.130s

gnome-terminal
# time ls -lR /etc
real    0m0.869s
user    0m0.057s
sys     0m0.141s

I ran this twice in both teminals and reported the
second result.

system info
P4 3.06 HT
2.6.7 SMP/SMT/HIGHMEM
1GB ram

-------------------------------------------------
Darren Williams <dsw AT gelato.unsw.edu.au>
Gelato@UNSW <www.gelato.unsw.edu.au>
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