Messages in this thread | | | Date | Mon, 14 Nov 2005 12:34:42 +0100 | From | Jens Axboe <> | Subject | Re: [2.6 patch] i386: always use 4k stacks |
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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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