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Re: [Qemu-devel] [PATCH v4 00/10] main-loop: switch to g_poll(3) on POSI


From: Stefan Hajnoczi
Subject: Re: [Qemu-devel] [PATCH v4 00/10] main-loop: switch to g_poll(3) on POSIX hosts
Date: Thu, 21 Feb 2013 16:33:52 +0100
User-agent: Mutt/1.5.21 (2010-09-15)

On Thu, Feb 21, 2013 at 02:17:14PM +0100, Christian Borntraeger wrote:
> On 20/02/13 11:28, Stefan Hajnoczi wrote:
> > Amos Kong <address@hidden> reported that file descriptors numbered higher
> > than 1024 could crash QEMU.  This is due to the fixed size of the fd_set 
> > type
> > used for select(2) event polling.
> > 
> 
> Good to see somebody working on that.
> We have just faced this problem on s390 after we have experimentally enabled 
> ioeventfd
> for virtio-ccw. We have several scenarios were we want > 600 devices for the 
> guest
> and the select loops then fails horribly because we exceed the 1024 fd 
> barrier.
> 
> So this looks like it could become a bugfix for that problem.
> 
> In terms of scalability it is probably better to have multiple threads that 
> poll on their 
> fds, instead of having one i/o thread. 

I think we'll get there, I'm currently working on adding multiple event
loop support to QEMU.

Stefan



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