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

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Date:	Fri, 15 Jun 2012 12:29:45 +0800
From:	Changli Gao <xiaosuo@...il.com>
To:	Li Yu <raise.sail@...il.com>
Cc:	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, Jun 15, 2012 at 12:13 PM, Li Yu <raise.sail@...il.com> wrote:
> Hi,
>
>  We encounter a performance problem in a large scale computer
> cluster, which needs to handle a lot of incoming concurrent TCP
> connection requests.
>
>  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.
>
>  I also asked some experienced webserver/proxy developers in my team
> for suggestions, it seem that behavior of many userland programs already
> called accept() multiple times after it is waked up by
> epoll_wait(). And the common action is adding the fd that accept()
> return into epoll interface by epoll_ctl() syscall then.
>
>  Therefore, I think that we'd better to introduce to batch variants of
> accept() and epoll_ctl() syscall, just like sendmmsg() or recvmmsg().
>
>  For accept(), we may need a new syscall, it may like this,
>
>  struct accept_result {
>      int fd;
>      struct sockaddr addr;
>      socklen_t addr_len;
>  };
>
>  int maccept4(int fd, int flags, int nr_accept_result, struct
> accept_result *results);
>
>  For epoll_ctl(), there are two means to extend it, I prefer to extend
> current interface instead of introduce to new syscall. We may introduce
> to a new flag EPOLL_CTL_BATCH. If userland call epoll_ctl() with this
> flag set, the meaning of last two arguments of epoll_ctl() change, .e.g:
>
>  struct batch_epoll_event batch_event[] = {
>         {
>              .fd = a_newsock_fd;
>              .epoll_event = { ... };
>         },
>         ...
>  };
>
>  ret = epoll_ctl(fd, EPOLL_CTL_ADD|EPOLL_CTL_BATCH, nr_batch_events,
> batch_events);
>

I think it is good idea. Would you please implement a prototype and
give some numbers? This kind of data may help selling this idea.
Thanks.

-- 
Regards,
Changli Gao(xiaosuo@...il.com)
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