But the whole point is that the notion of a "register" is wrong in
the
first place. [...]
forget about it then. The thing we "register" is dead-simple:
struct async_head_user {
struct syslet_uatom __user **completion_ring;
unsigned long ring_size_bytes;
unsigned long max_nr_threads;
};
this can be passed in to sys_async_exec() as a second pointer, and the
kernel can put the expected-completion pointer (and the user ring idx
pointer) into its struct atom. It's just a few instructions, and
only in
the cachemiss case.
that would make completions arbitrarily split-up-able. No registration
whatsoever. A waiter could specify which ring's events it is
interested
in. A 'ring' could be a single-entry thing as well, for a single
instance of pending IO.
I like this, too. (Not surprisingly, having outlined something like
it in a mail in one of the previous threads :)).
I'll bring up the POSIX AIO "list" IO case. It wants to issue a
group of IOs and sleep until they all return. Being able to cheaply
instantiate a ring implicitly with the submission of the IO calls in
the list will make implementing this almost too easy. It'd obviously
just wait for that list's ring to drain.
I hope. There might be complications around the edges (waiting for
multiple list IOs to drain?), but it seems like this would be on the
right track.
I might be alone in caring about having a less ridiculous POSIX AIO
interface in glibc, though, I'll admit. It seems like it'd be a
pretty sad missed opportunity if we rolled a fantastic general AIO
interface and left glibc to still screw around with it's own manual
threading :/.
- z
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