[PATCH] s3:events: Call all ready fd event handlers on eachiteration of the main loop

[Steven Danneman]

> On Mon, Jul 05, 2010 at 06:01:17PM -0700, Steven Danneman wrote:
> > Attached is a proposed patch to make the main message loop in S3
more
> > fair to fd based events.  Currently, network traffic can starve out
> > all other fd based events. We hit this at Isilon with our fd based
> > oplock upcalls, but this issue should also affect iNotify on Linux
> and
> > oplocks on Irix.
> >
> > As this is a major change to the server I wanted to pass it by the
> > list first.
> 
> Sorry, but I think this is the wrong fix. We deliberately only handle
> one single event in run_events. The reason is that while handling
> events the state of other pending events can change. This has caused
us
> big pain in the past.
> 
> Yes, this is indeed a problem that I had to badly work around with
> d5cf648, but the fix needs to look a bit differently I think. We need
> to remove a file descriptor off the list of interested fd's whenever
it
> is being handled.
> When either no fd's are left or in a select call nobody is active, we
> need to push all ones on the list again. This should give us round-
> robin handling of fds.
> 
> I am not sure if only select is affected. It might be the case that
> Linux under epoll is already fair in the sense that it never starves
> sockets.
> 
> Anybody around knowing for sure?
> 
> Volker

Hey Volker,

Taking the design considerations you mentioned I've reworked my patch.
It is not the Cadillac solution, as it only handles the smbd/select
case, but I went for minimal code disruption.

This patch effectively changes the select loop in smbd child process
only, to safely iterate through all fds returned by select each time,
while still handling timed and signal events round-robin.

This passes make test and I'm throwing more intensive work loads at it
now to test it's stability.

I've also opened bug 7686 to track this issue.  Please tell me what you
think.

-Steven 
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