Messages in this thread |  | | | From | (Eric W. Biederman) | | Date | Thu, 10 Jul 2008 13:17:54 -0700 | | Subject | Re: [RFC 00/15] x86_64: Optimize percpu accesses |
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Mike Travis <travis@sgi.com> writes:
> The biggest growth came from moving all the xxx[NR_CPUS] arrays into > the per cpu area. So you free up a huge amount of unused memory when > the NR_CPUS count starts getting into the ozone layer. 4k now, 16k > real soon now, ??? future?
Hmm. Do you know how big a role kernel_stat plays.
It is a per cpu structure that is sized via NR_IRQS. NR_IRQS is by NR_CPUS. So ultimately the amount of memory take up is NR_CPUS*NR_CPUS*32 or so.
I have a patch I wrote long ago, that addresses that specific nasty configuration by moving the per cpu irq counters into pointer available from struct irq_desc.
The next step which I did not get to (but is interesting from a scaling perspective) was to start dynamically allocating the irq structures.
Eric
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