linux-kernel - Re: [take24 0/6] kevent: Generic event handling mechanism.

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Date:	Mon, 20 Nov 2006 11:51:59 +0300
From:	Evgeniy Polyakov <johnpol@....mipt.ru>
To:	Andrew Morton <akpm@...l.org>
Cc:	Ulrich Drepper <drepper@...hat.com>,
	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	Zach Brown <zach.brown@...cle.com>,
	Christoph Hellwig <hch@...radead.org>,
	Chase Venters <chase.venters@...entec.com>,
	Johann Borck <johann.borck@...sedata.com>,
	linux-kernel@...r.kernel.org, Jeff Garzik <jeff@...zik.org>,
	Alexander Viro <aviro@...hat.com>
Subject: Re: [take24 0/6] kevent: Generic event handling mechanism.

On Mon, Nov 20, 2006 at 12:43:01AM -0800, Andrew Morton (akpm@...l.org) wrote:
> > > >If thread calls kevent_wait() it means it has processed previous entries, 
> > > >one can call kevent_wait() with $num parameter as zero, which
> > > >means that thread does not want any new events, so nothing will be
> > > >copied.
> > > 
> > > This doesn't solve the problem.  You could only request new events when 
> > > all previously reported events are processed.  Plus: how do you report 
> > > events if the you don't allow get_event pass them on?
> > 
> > Userspace should itself maintain order and possibility to get event in
> > this implementation, kernel just returns events which were requested.
> 
> That would mean that in a multithreaded application (or multi-processes
> sharing the same MAP_SHARED ringbuffer), all threads/processes will be
> slowed down to wait for the slowest one.

Not at all - all other threads can call kevent_get_events() with theirs
own place in the ring buffer, so while one of them is processing an
entry, others can fill next entries.

> > > >They all already imeplemented. Just all above, and it was done several
> > > >months ago already. No need to reinvent what is already there.
> > > >Even if we will decide to remove kevent_get_events() in favour of ring
> > > >buffer-only implementation, winting-for-event syscall will be
> > > >essentially kevent_get_events() without pointer to the place where to
> > > >put events.
> > > 
> > > Right, but this limitation of the interface is important.  It means the 
> > > interface of the kernel is smaller: fewer possibilities for problems and 
> > > fewer constraints if in future something should be changed (and smaller 
> > > kernel).
> > 
> > Ok, lets see for ring buffer implementation right now, and then we will
> > decide if we want to remove or to stay with kevent_get_events() syscall.
> 
> I agree that kevent_get_events() is duplicative and we shouldn't need it. 
> Better to concentrate all our development effort on the single and most
> flexible means of delivery.

Let's wait for ring buffer imeplementation first :)

-- 
	Evgeniy Polyakov
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