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From "Rana Dasgupta" <rdasg...@gmail.com>
Subject Re: [drlvm] Re: [design] Class unloading: false sharing of vtable marks
Date Tue, 14 Nov 2006 16:08:12 GMT
On 11/14/06, Robin Garner <robin.garner@anu.edu.au> wrote:
>
>
> >Whether this helps performance depends on the cache policy of the
> >multiprocessor.  I'm not sufficiently versed in cache architectures to
> >say, but I would expect that machines with sufficiently weak memory
> >models will make this cheap, those without will be expensive.


Salikh points out an interesting issue, but I think that this may be subject
to some assumptions about  SMP and hypertheaded architectures, and prevalent
L2 sharing models, at least on certain processors. This is a rapidly
changing area and as Weldon points out, the best approach may be to do the
prototype, and then run analytical tools to identify the pathologies and
tweak accordingly. Upfront, the overhead of a level of indirection, the
benefits of sharing the same cache line as the gcmap ptr and the cost of the
false sharing on some architectures is diffcult to figure out without
prototyping.

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