Messages in this thread | | | Date | Sun, 12 Aug 2007 05:17:10 +0200 | From | Rene Herman <> | Subject | Re: Are we properly prepared to handle 3 Socket setups? |
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On 08/12/2007 03:52 AM, Jesper Juhl wrote:
> On 12/08/07, Rene Herman <rene.herman@gmail.com> wrote: >> On 08/12/2007 03:08 AM, Jesper Juhl wrote: >> >>> This may be a little off topic, but I think it's interresting enough >>> to warrent a single mail. >>> >>> I just saw a news article (http://www.theinquirer.net/?article=41610) >>> about a 3 Socket Opteron motherboard and couldn't help but wonder if >>> we are prepared to deal with such a beast, so I thought I'd inform >>> everyone :-) >>> >>> I'm guessing equipping such a board with 3 single core CPU's could >>> show up some interresting corner cases in schedular code and >>> elsewhere, I'll bet we have some assumptions somewhere about >>> nr_of_cpus being an even number... >> I would hope the N=1 case will have flushed out enough of those... :-| >> > Hehe, true, but I was thinking more of nr_of_cpus is an odd number > 1. :-) > Just thinking of having to divide things by 3 makes me worry ;-) ...
It's not a hugely strange worry no. Grepping around (for num_online_cpus for example) didn't throw up any glaring bugs I believe.
A possible problem in mm/vmstat.c:calculate_threshold() where 3 CPUs would be treated as 2 through an fls(). No idea about that code and if that would be a problem.
The line just below where it does that _does_ seem to have a problem:
/* * Maximum threshold is 125 */ threshold = min(125, threshold);
as either the comment or the code is wrong and it seems it's the code. Added Andrew Morton to the CC for that.
CFS (v19.1) has an ilog2 on num_online_cpus() in kernel/sched.c:sched_init_granularity() but this seems not a problem. Added Ingo Molnar.
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