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DateTue, 19 Mar 2002 05:58:29 -0300 (BRT)
FromRik van Riel <>
SubjectRe: Scalability problem (kmap_lock) with -aa kernels
On Mon, 18 Mar 2002, Martin J. Bligh wrote:

> OK, I finally got the -aa kernel series running in conjunction with the
> NUMA-Q discontigmem stuff. For some reason which I haven't debugged
> yet 2.4.19-pre3-aa2 won't boot on the NUMA-Q even without the discontigmem
> stuff in ... so I went back to 2.4.19-pre1-aa1, which I knew worked from
> last time around (thanks again for that patch).
>
> So just comparing aa+discontigmem to standard 2.4.18+discontigmem, I see
> kernel compile times are about 35s vs 26.5s ....

That's probably Andrea's pte-highmem code, which uses the
global kmap pool instead of doing cpu-local atomic kmaps.

He's been told about this becoming a scalability problem
but didn't believe it since I didn't have any numbers for
him.  Maybe he believes it now since you've measured it ;)


> standard:
>
>  23991 total                                      0.0257
>   7679 default_idle                             147.6731
>   3044 _text_lock_dcache                          8.7221
>   2340 _text_lock_swap                           43.3333
>   1160 do_anonymous_page                          3.4940
> ...
>    109 kmap_high                                  0.3028
>     46 _text_lock_highmem                  0.4071
>
> andrea:
>  38549 total                                      0.0405
>  13102 _text_lock_highmem                       108.2810
>   8627 default_idle                             165.9038
>   2578 kunmap_high                               14.3222
>   2556 kmap_high                                  6.0857
>   1242 do_anonymous_page                          3.2684
>   1052 _text_lock_swap                           22.8696

> Andrea - is this your new highmem pte stuff doing this?
> Or is that not even in your tree as yet? Would be a shame if that's
> the problem as I really want to get the highmem pte stuff - allows
> me to put processes pagetables on their own nodes ....

You really want the pte-highmem by Arjan and Ingo, which uses
kmap_atomic (which is CPU-local and doesn't suffer the same
scalability problem as the global kmap pool).

regards,

Rik
-- 
<insert bitkeeper endorsement here>

http://www.surriel.com/		http://distro.conectiva.com/

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