x86: Reduce Memory Usage and Inter-Node message traffic
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- v1 Latest6 patches 3 repliesIn review
Patches in v1 No applies recorded yet
| # | Subject and files | Size | Replies | Applied |
|---|---|---|---|---|
| 1/6 | x86: Convert cpu_core_map to be a per cpu variablearch/ arch/ arch/ +9 more | +64 | 0 replies | |
| 2/6 | x86: Convert cpu_sibling_map to be a per cpu variablearch/ arch/ arch/ +10 more | +50 | 0 replies | |
| 3/6 | x86: Convert x86_cpu_to_apicid to be a per cpu variablearch/ arch/ arch/ +9 more | +80 | 0 replies | |
| 4/6 | x86: Convert cpu_llc_id to be a per cpu variablearch/ arch/ arch/ +2 more | +16 | 1 reply | |
| 5/6 | x86: fix cpu_to_node referencesarch/ arch/ arch/ | +5 | 1 reply | |
| 6/6 | x86: acpi-use-cpu_physical_iddrivers/ | +1 | 1 reply |
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Cover letter [PATCH 0/6] x86: Reduce Memory Usage and Inter-Node message traffic
In x86_64 and i386 architectures most arrays that are sized using NR_CPUS lay in local memory on node 0. Not only will most (99%?) of the systems not use all the slots in these arrays, particularly when NR_CPUS is increased to accommodate future very high cpu count systems, but a number of cache lines are passed unnecessarily on the system bus when these arrays are referenced by cpus on other nodes.
Typically, the values in these arrays are referenced by the cpu accessing it's own values, though when passing IPI interrupts, the cpu does access the data relevant to the targeted cpu/node. Of course, if the referencing cpu is not on node 0, then the reference will still require cross node exchanges of cache lines. A common use of this is for an interrupt service routine to pass the interrupt to other cpus local to that node.
Ideally, all the elements in these arrays should be moved to the per_cpu data area. In some cases (such as x86_cpu_to_apicid) the array is referenced before the per_cpu data areas are setup. In this case, a static array is declared in the __initdata area and initialized by the booting cpu (BSP). The values are then moved to the per_cpu area after it is initialized and the original static array is freed with the rest of the __initdata.
Patches applied to: linux-2.6.23-rc2-mm2
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