netdev - Re: [RFC] Introduce to batch variants of accept() and epoll

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Date:	Fri, 15 Jun 2012 10:51:58 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Li Yu <raise.sail@...il.com>
Cc:	Changli Gao <xiaosuo@...il.com>,
	Linux Netdev List <netdev@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	davidel@...ilserver.org
Subject: Re: [RFC] Introduce to batch variants of accept() and epoll_ctl()
 syscall

On Fri, 2012-06-15 at 13:37 +0800, Li Yu wrote:

> Of course, I think that implementing them should not be a hard work :)
> 
> Em. I really do not know whether it is necessary to introduce to a new 
> syscall here. An alternative solution to add new socket option to handle 
> such batch requirement, so applications also can detect if kernel has 
> this extended ability with a easy getsockopt() call.
> 
> Any way, I am going to try to write a prototype first.

Before that, could you post the result of "perf top", or "perf
record ...;perf report"

>  The top shows the kernel is most cpu hog, the testing is simple,
> just a accept() -> epoll_ctl(ADD) loop, the ratio of cpu util sys% to
> si% is about 2:5.

This ratio is not meaningful, if we dont know where time is spent.


I doubt epoll_ctl(ADD) is a problem here...

If it is, batching the fds wont speed the thing anyway...

I believe accept() is the problem here, because it contends with the
softirq processing the tcp session handshake.



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