linux-kernel - Re: [patch 05/11] syslets: core code

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Message-ID: <20070215191059.GB23953@2ka.mipt.ru>
Date:	Thu, 15 Feb 2007 22:10:59 +0300
From:	Evgeniy Polyakov <johnpol@....mipt.ru>
To:	bert hubert <bert.hubert@...herlabs.nl>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Christoph Hellwig <hch@...radead.org>,
	Andrew Morton <akpm@....com.au>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Ulrich Drepper <drepper@...hat.com>,
	Zach Brown <zach.brown@...cle.com>,
	"David S. Miller" <davem@...emloft.net>,
	Benjamin LaHaise <bcrl@...ck.org>,
	Suparna Bhattacharya <suparna@...ibm.com>,
	Davide Libenzi <davidel@...ilserver.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [patch 05/11] syslets: core code

On Thu, Feb 15, 2007 at 07:46:56PM +0100, bert hubert (bert.hubert@...herlabs.nl) wrote:
> 1) batch, and wait for, with proper error reporting:
> 	socket();
> 	[ setsockopt(); ]
> 	bind();
> 	connect();
> 	gettimeofday();  // doesn't *always* happen
> 	send();
> 	recv();
> 	gettimeofday(); // doesn't *always* happen
> 
> 	I go through this sequence for each outgoing powerdns UDP query
> 	because I need a new random source port for each query, and I
> 	connect because I care about errrors. Linux does not give me random
> 	source ports for UDP sockets.

What about a setsockopt or just random port selection patch? :)

> 	When async, I can probably just drop the setsockopt (for
> 	nonblocking). I already batch the gettimeofday to 'once per epoll
> 	return', but quite often this is once per packet.
> 
> 2) 	On the client facing side (port 53), I'd very much hope for a way to
> 	do 'recvv' on datagram sockets, so I can retrieve a whole bunch of
> 	UDP datagrams with only one kernel transition.
> 
> 	This would mean that I batch up either 10 calls to recv(), or one
> 	'atom' of 10 recv's.
> 
> Both 1 and 2 are currently limiting factors when I enter the 100kqps domain
> of name serving. This doesn't mean the rest of my code is as tight as it
> could be, but I spend a significant portion of time in the kernel even at
> moderate (10kqps effective) loads, even though I already use epoll. A busy
> PowerDNS recursor typically spends 25% to 50% of its time on 'sy' load.
> 
> This might be due to my use of get/set/swap/makecontext though.

It is only about one syscall in get and set/swap context, btw, so it
should not be a main factor, doesn't it?

As an advertisement note, but if you have a lot of network events per epoll 
read try to use kevent - its socket notifications do not require
additional traverse of the list of ready events as in poll usage.

> 	Bert
> 
> -- 
> http://www.PowerDNS.com      Open source, database driven DNS Software 
> http://netherlabs.nl              Open and Closed source services

-- 
	Evgeniy Polyakov
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