Re: [Xen-users] [Xen-devel] 1000 Domains: Not able to access Domu via xm console from Dom0

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Sat, 2012-12-29 at 16:21 +0000, Wei Liu wrote:
> On Mon, 2012-12-17 at 11:56 +0000, Ian Campbell wrote:

> > I rather suspect this is overrunning the readfds array.
> > http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/sys_select.h.html 
> > suggests this is sized by FD_SETSIZE. On my system that appears to be 
> > statically 1024 (at least strace doesn't show a syscall to determine it in 
> > a simple test app although grep /usr/include suggests that might be an 
> > option on some systems).
> > 
> > It doesn't seem likely that there will be a simple solution to this. We
> > probably need to switch to something other than select(2). poll(2) seems
> > to handle arbitrary numbers of file descriptors. epoll(7) would be nice
> > (it supposedly scales better than poll) but is Linux specific. Another
> > option might be to fork multiple worker processes (might be a good idea
> > if xenconsole becomes a bottleneck).
> 
> libevent wraps around different event APIs and provides consistent
> interface across OSes. But I don't know whether adding libevent as Xen
> tools dependency is a good idea.

Using some reasonably widespread library to abstract away the
differences between Linux and *BSD here seems like a better idea than
rolling our own. I don't know enough about it to say if libevent fits
the bill or not.

Based on a cursory glance it seems like libevent implements a complete
event loop and requires the application to switch over to using it
entirely. This may not be a bad thing but it might be preferable (and/or
easier) to see if there is a library which only provides a basic simple
abstraction/wrapper over the various polling mechanisms.

Ian.


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