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To: JINMEI Tatuya / =?ISO-2022-JP?B?GyRCP0BMQEMjOkgbKEI=?=
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In-reply-to: Your message of "Tue, 15 Jul 2008 15:39:09 PDT."
	<m2skuag4c2.wl%Jinmei_Tatuya@isc.org> 
Date: Tue, 15 Jul 2008 16:09:17 -0700
From: Bakul Shah <bakul@bitblocks.com>
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Cc: freebsd-net@freebsd.org, Kris Kennaway <kris@FreeBSD.org>,
	Thomas Vogt <freebsdlists@bsdunix.ch>
Subject: Re: too many open file descriptors messages since bind 9.4.2-P1
	(port dns94) 
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On Tue, 15 Jul 2008 15:39:09 PDT JINMEI Tatuya / =?ISO-2022-JP?B?GyRCP0BMQEMjOkgbKEI=?= <Jinmei_Tatuya@isc.org>  wrote:
> At Tue, 15 Jul 2008 15:12:31 -0700,
> Bakul Shah <bakul@bitblocks.com> wrote:
> 
> > > Besides, I guess that the P1 versions severely suffer from heavy
> > > overhead of select(2) when it regularly opens more than 1000 sockets.
> > > Even if 'too many open file' messages are gone, many users won't
> > > accept the increased load due to the overhead.  Beta versions use
> > > kqueue, eliminating the fundamental overhead as well as the (too low)
> > > limitation of # of descriptors.
> > 
> > Or more portably you can use poll(2).
> 
> I've not played with poll(2) in BIND9, but as far as I understand it,
> it doesn't solve the fundamental overhead issue here.  For example,
> the application should examine all possible descriptors even if only a
> few of them are readable.

IIRC, when poll() returns n, you only look at the first n
values in the pollfd array so it is a win when you expect a
very small number of fds to be ready.  In the select case you
have to test the bit array until you see the last ready fd.

> Anyway, since this is a FreeBSD specific list, I believe we can safely
> assume the existence of kqueue, unless we are talking about a very old
> version:-)

Presumably kqueue has a lower cpu usage until the system gets
loaded at which point polling might win.