Re: [Qemu-devel] Linux kernel polling for QEMU

[Paolo Bonzini <pbonzini@redhat.com>]

> > > Maybe we could do the same for sockets?  When data is available on a
> > > socket (or when it becomes writable), write to a user memory location.
> > >
> > > I, too, have an interest in polling; in my situation most of the polling
> > > happens in userspace.
> >
> > You are trying to improve on the latency of non-blocking
> > ppoll(2)/epoll_wait(2) call?
> 
> Yes, but the concern is for throughput, not latency.
> 
> My main loop looks like
> 
>     execute some tasks
>     poll from many sources
> 
> Since epoll_wait(..., 0) has non-trivial costs, I have to limit the
> polling rate, and even so it shows up in the profile.  If the cost were
> lower, I could poll at a higher frequency, resulting in lower worst-case
> latencies for high-priority tasks.

IMHO, the ideal model wouldn't enter the kernel at all unless you _want_
to go to sleep.

Paolo