Re: [PATCH 5/5] aio-posix: make AioHandler dispatch O(1) with epoll

[Sergio Lopez <slp@redhat.com>]

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On Fri, Feb 14, 2020 at 05:17:12PM +0000, Stefan Hajnoczi wrote:
> File descriptor monitoring is O(1) with epoll(7), but
> aio_dispatch_handlers() still scans all AioHandlers instead of
> dispatching just those that are ready.  This makes aio_poll() O(n) with
> respect to the total number of registered handlers.
> 
> Add a local ready_list to aio_poll() so that each nested aio_poll()
> builds a list of handlers ready to be dispatched.  Since file descriptor
> polling is level-triggered, nested aio_poll() calls also see fds that
> were ready in the parent but not yet dispatched.  This guarantees that
> nested aio_poll() invocations will dispatch all fds, even those that
> became ready before the nested invocation.
> 
> Since only handlers ready to be dispatched are placed onto the
> ready_list, the new aio_dispatch_ready_handlers() function provides O(1)
> dispatch.
> 
> Note that AioContext polling is still O(n) and currently cannot be fully
> disabled.  This still needs to be fixed before aio_poll() is fully O(1).
> 
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>  util/aio-posix.c | 106 +++++++++++++++++++++++++++++++++--------------
>  1 file changed, 76 insertions(+), 30 deletions(-)

Reviewed-by: Sergio Lopez <slp@redhat.com>

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