linux-kernel - Re: [PATCH] epoll: Improved support for multi-threaded clients

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Message-ID: <20120709184539.GI7275@edge.cmeerw.net>
Date:	Mon, 9 Jul 2012 20:45:39 +0200
From:	Christof Meerwald <cmeerw@...erw.org>
To:	"Paton J. Lewis" <palewis@...be.com>
Cc:	Alexander Viro <viro@...iv.linux.org.uk>,
	Jason Baron <jbaron@...hat.com>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Paul Holland <pholland@...be.com>,
	Davide Libenzi <davidel@...ilserver.org>
Subject: Re: [PATCH] epoll: Improved support for multi-threaded clients

On Fri, Jun 29, 2012 at 02:43:06PM -0700, Paton J. Lewis wrote:
> At 6/19/2012 11:17 AM, Christof Meerwald wrote:
> >But, taking one step back - wouldn't an alternative approach be to add
> >some mechanism to allow a thread to post a user-event for an fd? So in
> >delete_epoll_item you would post a user event (e.g. EPOLLUSER) for the
> >fd which you can then handle in your epoll_wait processing thread -
> >with no additional synchronisation necessary.
> I think this is an excellent suggestion, and in fact your proposal
> is more similar to what Windows provides when solving this problem.
> I'll test this idea out with our code and get back to you. Is there
> an existing kernel technique that you would recommend for posting a
> user event for an fd, or should I explore using epoll_ctl with
> EPOLL_CTL_MOD?

I don't know about any existing kernel technique for this, but my gut
feeling would be a new op value for epoll_ctl, maybe something like
EPOLL_CTL_TRIGGER.


Christof

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