[cap-talk] - Bellizzomi - Capabilities and Shapiro's focus, Coyotos, etc.
Mark S. Miller
markm at cs.jhu.edu
Wed Nov 29 10:41:23 CST 2006
Karp, Alan H wrote:
> While you can't prevent wall banging, you can prevent wall listening by
> removing all forms of indeterminacy, such as access to the system clock.
> Any process that is deterministically replayable meets this criterion.
> Did I get that right, MarkM?
In addition, once such processes are deafened, this can contribute towards
alleviating wall banging in an indirect and imperfect way:
The main wall banging channel is variable resource use. The main defense
against such wall banging is preallocation of worst-case resources, and then
wasting the slack -- the difference between actual and worst-case resource
needs. Since typical resource needs can often be orders of magnitude less than
worst case, this waste can be quite costly.
However, if one has a bunch of deafened processes that could do useful batch
work, one can run these in the slack. As deafened processes, they can't sense
how much slack they're getting, or how this slack is spread over real time.
By "batch" above, the key feature is that no one needs an answer from these
promptly, so these answers can be delayed and aggregated. Revealing which
answers are available at some future time does reveal some covert info, but
hey, I said it was imperfect.
Text by me above is hereby placed in the public domain
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