Re: [patch 00/13] Syslets, "Threadlets", generic AIO support, v3

Ingo Molnar
2007-02-22T14:43:28Z

* Suparna Bhattacharya <suparna@in.ibm.com> wrote:

> > maybe it will, maybe it wont. Lets try? There is no true difference
> > between having a 'request structure' that represents the current
> > state of the HTTP connection plus a statemachine that moves that
> > request between various queues, and a 'kernel stack' that goes in
> > and out of runnable state and carries its processing state in its
> > stack - other than the amount of RAM they take. (the kernel stack is
> > 4K at a minimum - so with a million outstanding requests they would
> > use up 4 GB of RAM. With 20k outstanding requests it's 80 MB of RAM
> > - that's acceptable.)
>
> At what point are the cachemiss threads destroyed ? In other words how
> well does this adapt to load variations ? For example, would this 80MB
> of RAM continue to be locked down even during periods of lighter loads
> thereafter ?

you can destroy them at will from user-space too - just start a slow
timer that zaps them if load goes down. I can add a
sys_async_thread_exit(nr_threads) API to be able to drive this without
knowing the TIDs of those threads, and/or i can add a kernel-internal
mechanism to zap inactive threads. It would be rather easy and
low-overhead - the v2 code already had a max_nr_threads tunable, i can
reintroduce it. So the size of the pool of contexts does not have to be
permanent at all.

Ingo