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

Davide Libenzi
2007-02-22T19:38:10Z

On Thu, 22 Feb 2007, Ingo Molnar wrote:

>
> * Ulrich Drepper <drepper@redhat.com> wrote:
>
> > Ingo Molnar wrote:
> > > in terms of AIO, the best queueing model is i think what the kernel uses
> > > internally: freely ordered, with barrier support.
> >
> > Speaking of AIO, how do you imagine lio_listio is implemented? If
> > there is no asynchronous syscall it would mean creating a threadlet
> > for each request but this means either waiting or creating
> > several/many threads.
>
> my current thinking is that special-purpose (non-programmable, static)
> APIs like aio_*() and lio_*(), where every last cycle of performance
> matters, should be implemented using syslets - even if it is quite
> tricky to write syslets (which they no doubt are - just compare the size
> of syslet-test.c to threadlet-test.c). So i'd move syslets into the same
> category as raw syscalls: pieces of the raw infrastructure between the
> kernel and glibc, not an exposed API to apps. [and even if we keep them
> in that category they still need quite a bit of API work, to clean up
> the 32/64-bit issues, etc.]

Now that chains of syscalls can be way more easily handled with clets^wthreadlets,
why would we need the whole syslets crud inside?
Why can't aio_* be implemented with *simple* (or parallel/unrelated)
syscall submit w/out the burden of a complex, limiting and heavy API (I
won't list all the points against syslets, because I already did it
enough times)? The compat layer only is so bad to not be even funny.
Look at the code. Only removing the syslets crud would prolly cut 40% of
it. And we did not even touch the compat code yet.

- Davide