> Jason Wang <jasowang@xxxxxxxxxx> wrote on 01/25/2016 05:00:05 AM:
> On 01/24/2016 05:00 PM, Mike Rapoport wrote:
> > Hi Jason,
> >
> >> Jason Wang <jasowang <at> redhat.com> writes:
> >>
> >> Hi all:
> >>
> >> This series tries to add basic busy polling for vhost net. The idea is
> >> simple: at the end of tx/rx processing, busy polling for new tx added
> >> descriptor and rx receive socket for a while.
> > There were several conciens Michael raised on the Razya's attempt to add
> > polling to vhost-net ([1], [2]). Some of them seem relevant for these
> > patches as well:
> >
> > - What happens in overcommit scenarios?
>
> We have an optimization here: busy polling will end if more than one
> processes is runnable on local cpu. This was done by checking
> single_task_running() in each iteration. So at the worst case, busy
> polling should be as fast as or only a minor regression compared to
> normal case. You can see this from the last test result.
>
> > - Have you checked the effect of polling on some macro benchmarks?
>
> I'm not sure I get the question. Cover letters shows some benchmark
> result of netperf. What do you mean by "macro benchmarks"?
Back then, when Razya posted her polling implementation, Michael had concern about the macro effect ([3]),
so I was wondering if this concern is also valid for your implementation.
Now, after I've reread your changes, I think it's not that relevant...
> >> The maximum number of time (in us) could be spent on busy polling was
> >> specified ioctl.
> > Although ioctl is definitely more appropriate interface to allow user to
> > tune polling, it's still not clear for me how *end user* will interact with
> > it and how easy it would be for him/her.
>
> There will be qemu part of the codes for end user. E.g. a vhost_poll_us
> parameter for tap like:
>
> -netdev tap,id=hn0,vhost=on,vhost_pull_us=20
Not strictly related, I'd like to give a try to polling + vhost thread sharing and polling + workqueues.
Do you mind sharing the scripts you used to test the polling?
Thanks,
Mike.
> Thanks
>
> >
> > [1] http://thread.gmane.org/gmane.linux.kernel/1765593
> > [2] http://thread.gmane.org/gmane.comp.emulators.kvm.devel/131343
> >
> > --
> > Sincerely yours,
> > Mike.
> >
[3] https://www.mail-archive.com/kvm@xxxxxxxxxxxxxxx/msg109703.html
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