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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