Message-ID: <3C0F1F32.C235F9CC@kegel.com>
Date: Wed, 05 Dec 2001 23:33:06 -0800
From: Dan Kegel <dank@kegel.com>
MIME-Version: 1.0
To: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Carlo Wood <carlo@alinoe.com>
Subject: re: kqueue, kevent - kernel event notification mechanism
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Sender: linux-kernel-owner@vger.kernel.org

Carlo Wood <carlo@alinoe.com> wrote:
> are there any plans to implement the kqueue, kevent system calls
> in the linux kernel?
> 
> There is no substitute for them currently; select() and poll()
> both suffer from dramatic cpu usage when a daemon is loaded with
> a few thousand clients.

There is already an efficient mechanism - although with a very
different interface - in the 2.4.x kernel: edge triggered readiness
notification via realtime signals.  This matches one style of
kqueue()/kevent() usage.  For those who prefer level-triggered
readiness notification (more like what poll() gives you),
I have written a wrapper class that papers over the difference
efficiently, at the cost of making the app tell my class about
all the EWOULDBLOCKs it gets.
See http://www.kegel.com/c10k.html#nb.sigio for details.
I don't particularly like signals for this, as they're a
bit heavyweight, and the global signal queue is a bit precious,
but it does benchmark well, even for thousands of clients.

(That page also describes kqueue etc. and the experimental
/dev/poll drivers.)
- Dan
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