Re: [RFC] Introduce to batch variants of accept() and epoll_ctl()syscall

[Li Yu]

ä 2012å06æ15æ 12:29, Changli Gao åé:
> On Fri, Jun 15, 2012 at 12:13 PM, Li Yu<raise.sail@xxxxxxxxx>  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.

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.

Thanks

Yu
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