(restored 'CC, sorry for dropping it originally, Notes is still hard for 
me)

Jason Wang [off-list ref] wrote on 01/25/2016 05:00:05 AM:
On 01/24/2016 05:00 PM, Mike Rapoport wrote:

quoted

Hi Jason,

quoted

Jason Wang <jasowang <at> redhat.com> writes:

Hi all:

This series tries to add basic busy polling for vhost net. The idea 

is

quoted

quoted

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

quoted

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.

quoted

- 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...

quoted

quoted

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

quoted

tune polling, it's still not clear for me how *end user* will interact 

with

quoted

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

quoted

[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@vger.kernel.org/msg109703.html