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

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Date:	Mon, 20 Nov 2006 01:15:16 -0800
From:	Andrew Morton <akpm@...l.org>
To:	Evgeniy Polyakov <johnpol@....mipt.ru>
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, 20 Nov 2006 11:51:59 +0300
Evgeniy Polyakov <johnpol@....mipt.ru> wrote:

> 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.

eh?  That's not a ringbuffer, and it sounds awfully complex.

I don't know if this (new?) proposal resolves the
events-gets-lost-due-to-thread-cancellation problem?  Would need to see
considerably more detail.

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