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    SubjectRe: [2.6 patch] i386: always use 4k stacks
    On Mon, Nov 14 2005, Arjan van de Ven wrote:
    > On Mon, 2005-11-14 at 12:24 +0100, Jens Axboe wrote:
    > > >
    > > > not sure; I do know that it very much helps java (many more threads
    > > > possible) and the VM (far less order 1 allocs). In addition the 4Kb
    > > > allocation can be satisfied with the per cpu list of free 4Kb pages,
    > > > while obviously an order 1 cannot and has to go global.
    > >
    > > I realize it has nice advantages in theory, just wondering if anyone has
    > > done a performance analysis of 4kb vs 8kb stacks lately (or at all?).
    > I don't think at least anyone at RH has done any; the functionality gain
    > was already enough for us. One item I missed: in the many-thread cases,
    > you also save a lot of memory that can now be used for pagecache;
    > this won't of course be visible in a microbenchmark but should help
    > system wide.
    > Also in the implementation I don't see any way 4Kb stacks could show up
    > in any benchmarks as negative; there are only 4 or 5 extra instructions
    > in any path, and afaics no cache downsides (in fact the same irq stack
    > memory is now reused for irqs instead of threadstack-du-jour, so less
    > footprint/hotter caches)

    The only downside is the potential crashes due to overflowing the stack,
    I'm not worried about 4kb stacks performing worse.

    Jens Axboe

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