Re: [patch 05/11] syslets: core code

[Evgeniy Polyakov]

On Thu, Feb 15, 2007 at 07:46:56PM +0100, bert hubert (bert.hubert@xxxxxxxxxxxxx) 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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