Re: [PATCH 5/5] ioeventfd: Introduce KVM_IOEVENTFD_FLAG_SOCKET

Sasha Levin
2011-07-14T08:07:31Z

On Thu, 2011-07-14 at 10:26 +0300, Pekka Enberg wrote:
> On 07/13/2011 04:00 PM, Pekka Enberg wrote:
> >> On Wed, Jul 13, 2011 at 3:57 PM, Avi Kivity<avi@redhat.com> wrote:
> >> >> We'd like to keep 8250 emulation because it's the most robust method
> >> >> for getting data out of the kernel when there's problems. It's also
> >> >> compatible with earlyprintk and such.
> >> >
> >> > What do you hope to gain from the optimization? 100ms less boot time?
> >>
> >> Hmm? I use serial console for logging into the guest and actually
> >> using it all the time.
>
> On 7/13/11 4:32 PM, Avi Kivity wrote:
> > Just how fast do you type?
> >
> > It's not enough to make something faster, it has to be slow to being
> > with. The interface is good, but use it where it helps.
>
> I don't know why you bring up serial console input here. Sasha's
> original KVM_IOEVENTFD_FLAG_PIPE patch clearly stated:
>
> A simple example for practical use is the serial port. we are not
> interested in an exit every time a char is written to the port, but
> we do need to know what was written so we could handle it on the
> guest.
>
> So it's talking about the serial console output, not input.

Yes, I have originally thought of doing the pipefd interface to prevent
the overhead caused by console intensive benchmarks on actual
benchmarks. It's funny how much slowness spinning the cursor or printing
a table incurs.

--

Sasha.