Messages in this thread | | | From | (Linus Torvalds) | Subject | Re: [Lse-tech] Re: 10.31 second kernel compile | Date | Thu, 14 Mar 2002 19:05:50 +0000 (UTC) |
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In article <87wuwfxp25.fsf@fadata.bg>, Momchil Velikov <velco@fadata.bg> wrote: > >Out of curiousity, why there's a need to update the linux page tables ? >Doesn't pte/pmd/pgd family functions provide enough abstraction in >order to maintain _only_ the hashed page table ?
No. The IBM hashed page tables are not page tables at all, they are really just a bigger 16-way set-associative in-memory TLB.
You can't actually sanely keep track of VM layout in them.
Those POWER4 machines are wonderful things, but they have a few quirks:
- it's so expensive that anybody who is slightly price-conscious gets a farm of PC's instead. Oh, well.
- the CPU module alone is something like .5 kilowatts (translation: don't expect it in a nice desktop factor, even if you could afford it).
- IBM nomenclature really is broken. They call disks DASD devices, and they call their hash table a page table, and they just confuse themselves and everybody else for no good reason. They number bits the wrong way around, for example (and big-endian bitordering really _is_ clearly inferior to little-endian, unlike byte-ordering. Watch the _same_ bits in the _same_ register change name in the 32 vs 64-bit architecture manuals, and puke)
But with all their faults, they do have this really studly setup with 8 big, fast CPU's on a single module. A few of those modules and you get some ass-kick performance numbers. As you can see.
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